D.N. Basov\, Professor of Physics\, Columbia University
Shedding nano-light on quantum materialsWhat Are 2D and Topological Materials Good For?
I will discuss whether 2D semiconductors and topological semimetals could play a role in future electronics. Their ultra thin nature provides some advantages for flexible electronics [1]\, light-w eight solar cells [2]\, nanoscale transistors [3]\, and interconnects [4]\, but they are not ideal where conventional materials work sufficiently well . I will dive deeper into monolayer 2D semiconductors as energy-efficient t ransistors [5-8]\, discuss the effects of strain on their operation [8\,9]\ , and outline fundamental challenges that remain. I will also describe ultr athin chalcogenides for phase-change memory [10] and ultrathin topological semimetals as future interconnects [4]. If time permits\, I will discuss po tential thermal management advances using 2D materials [12\,13] and nitride s with good thermal conductivity [14]. Combined\, these studies reveal some fundamental limits and practical applications of emerging materials for fu ture electronics.
[1] A. Daus et al.\, Nat. Elec. (2021). [2] K.N. Nazif\, et al.\, Comm. Phys. (2023). [3] C. English et al.\, IEDM (20 16). [4] A.I. Khan et al.Science (2025). [5] C. McClellan et al. ACS Nano ( 2021). [6] R.Bennett &\; E. Pop\, Nano Lett. (2023). [7] J.-S. Ko et al. \, IEEE-TED(2025). [8] I. Datye et al.\, Nano Lett. (2022). [9] M. Jaikisso on et al.\, Nat. Elec. (2024). [10] X.Wu et al. Nat. Comm. (2024). [12] S.V aziri et al.\, Science Adv. (2019). [13] M. Chen et al.\, 2D Mat. (2021). [ 14] C. Koroglu&\; E. Pop\, EDL (2023).
ZOOM link: https://umd.zoom.us/j/92 495875521
Host: Cheng Gong
"Renormalized masses and their effects on transport in corre lated metals.”
This talk will present our recent re sults using optical spectroscopy on two different correlated metals\, the c uprate high temperature superconductors and the heavy fermion CeCoIn5. The recent observation of cyclotron resonance in optimally-doped La2−xSrxCuO4 using time-domain THz spectroscopy in high magnetic field has given new pos sibilities for the study of cuprate superconductors. I will present the me asurement of the cyclotron mass of the hole doped cuprate La2−xSrxCuO4 acro ss a range of dopings spanning the slightly underdoped (x=0.13) to highly o verdoped (x=0.26)\, near to the termination of the superconducting dome. Th ese results reveal a systematic increase of mc with doping\, up to values g reater than thirteen times the bare electron mass. This is in contrast with those masses extracted from the heat capacity\, which show a peak near the pseudogap critical point p∗ and/or Lifshitz transition. Among other aspect s\, these results are surprising as photoemission reveals a Lifshitz transi tion in the middle of our doping range and the sign of the cyclotron mass d etermined from a finite frequency resonance is -- in conventional theories — a topological quantity only sensitive to whether or not the Fermi surface is closed around holes or electrons. We see no sign of a divergence of the mass near p∗ nor near the Lifshitz transition\, showing that any singulari ty -- if it exists -- is not strong enough to affect the cyclotron mass. I will also discuss our recent work on thin films of the heavy-fermion super conductor CeCoIn_5. The complex optical conductivity is analyzed through a Drude model and extended Drude model analysis. Below the 40 K Kondo cohere nce temperature\, a narrow Drude-like peak forms\, as the result of the $f$ orbital-conduction electron hybridization and the formation of the heavy-f ermion state. Its width shows a T^2 dependence giving evidence for a hidden Fermi state.
Spin transport and spin-orbit torque in metallic hete rostructures
Current-induced spin-orbit torque enabl es electric control of magnetization in spintronic devices. I will start by discussing the basic phenomenology and mechanisms of spin-orbit torque. I will then discuss first-principles calculations of spin transport and spin- orbit torques in disordered films and multilayers using the nonequilibrium Green's function technique [1]. Of particular interest is the generation of spin-orbit torque with unconventional spin polarization that can enable th e switching of magnetization perpendicular to the film plane\; this require s certain symmetries to be broken. I will discuss unconventional torques in ferromagnet/nonmagnet/ferromagnet trilayers [2]\, as well as spin currents generated by the so-called spin-splitting effect in alter magnets [3] and anisotropic ferromagnets [4]\, which could be harnessed for this purpose.
[1] K. D.Belashchenko\, A. A. Kovalev\, and M. van Schilfgaarde \, Phys. Rev.Materials 3\, 011401(R) (2019)\; Phys. Rev . B 101\,020407(R) (2020).
[2] V. P. Amin\,G. G. Baez Flores\, A. A. Kovalev\, and K. D. Belashchenko\, Phys. R ev. B 110\,214427 (2024).
[3] K. D.Belashc henko\, Phys. Rev. Lett. 134\, 086701 (2025).
[4] K. D.Belashc henko\, Phys. Rev. B 109\, 054409 (2024).
Title: Designing FerroelectricNanocomposites/Nano hete rojunctions for Clean Energy Harvesting
With the ever-increas
ing demand for energy and also due to an increase in environmental pollutio
n\, there has been a lot of interest to develop novel materials for clean e
nergy generation. Harvesting vibration energy through piezo/tribogenerator
[1-4]\, and hydrogen generation through photoelectrochemical water splittin
g are among the promising environmentally friendly approach to providing so
lutions to the present problem. We have designed several ferroelectric nano
composite/nanostructures and explored its potential application for efficie
nt piezo/tribo generators and as photoanodes for PEC water splitting.
Triboelectric effect based nanogenerator have the edge over other mec hanical energy harvesters because of its robustness\, cost-effectiveness an d higher energy. In the solid-solid interface based tribo-nanogenerator bot h the material used for contact are solid [1\,2] whereas in the solid-liqui d interface based tribo-nanogenerator liquid (water drop)comes in contact w ith a solid material [3]. The performance of these tribo-nanogenerator depe nds upon the amount of induced charges during the contact and the retentive ly of these charges which can be captured for generating electricity. In t he Photoelectrochemical water splitting device use of ferroelectric nanocom posite/heterostructures enabled to tune of the band edge position and thus results in much-improved efficiency [5].
The present talk wil l review the progress made so far in our group at IIT Delhi in the above-me ntioned area [2-6] and will also present the main challenges.
Reference:
[1] H. H. Singh and N. Khare\, Nano Energy\,52\, 216-222 (2018)
[2] H. H. Singh and N. Khare\, Energy\, 178\,765-771 (2019)
[3] H. H. Singh and N. Khare\, AdvancedMaterials Interfaces\, 8\, 21700 68 (2021)
[4] A. Mondal\, M. Faraz\, N. Khare\, AppliedPhysics Letter s\, 121\, 103901 (2022)
[5] D. Kumar\, S. Sharma\, N. Khare\, Renewab leEnergy\, 163\, 1569-1579 (2021)
[6] AK Gautam\, HH Singh\, N Khare\ , Nano Energy 107\,108125 (2023)
Host: Steve A nlage
LAST-MODIFIED:20231004T035747Z LOCATION:Room 0360 in Toll/Physics SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC Special Seminar - Neeraj Khare\, Indian Institute of Technology \, New Delhi TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20170223T140000 DTEND;TZID=America/New_York:20170223T153000 DTSTAMP:20260524T204340Z UID:ua8bnb6fr09o4ste1b9vrnc0e8@google.com RECURRENCE-ID;TZID=America/New_York:20170223T140000 CREATED:20160624T143638Z DESCRIPTION:SPEAKER: Paul Haney\, NIST\n\nTITLE: Polycrystalline Photovol taics: grain boundaries and spin-orbit coupling.\n\nABSTRACT: Despite deca des of research\, the role of grain boundaries in the photovoltaic behavior of thin film polycrystalline solar cells remains poorly understood. The c omplex morphology of grain boundaries and the nonlinear behavior of these m aterials have so far precluded an analytical description of their photovolt aic response. This in turn has hindered interpretation of experiments and efforts to optimize system design and materials. I’ll present our recent a nalysis in which we derive an analytical form for the dark J-V relation for a polycrystalline pn+ junction with an array of grain boundaries of varyin g orientation and defect structure. This relation enables an expression of the solar cell open circuit voltage in terms of grain boundary properties\ , which may point the way to improving this figure of merit for thin film m aterials such as CdTe. \n\nThe organic-inorganic lead halide perovskite is another high efficiency polycrystalline solar cell receiving much recent at tention. Under conditions of reduced crystal symmetry\, the perovskite is an example of a 3-d Rashba material. I’ll present our recent exploration o f the spin-dependent optical response of 3-d Rashba materials\, and show th at this response may reveal the role of grain boundaries in photovoltaic re sponse. I’ll finally discuss some unique aspects of the optical control of magnetism in ferromagnetic 3-d Rashba materials.\n\nHOST: Victor Yakovenko LAST-MODIFIED:20170203T151543Z LOCATION:Rm 1201 John S Toll Physics Bldg SEQUENCE:0 STATUS:CONFIRMED SUMMARY:CNAM COLLOQUIUM: Paul Haney\, NIST TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20220310T140000 DTEND;TZID=America/New_York:20220310T153000 DTSTAMP:20260524T204340Z UID:7gbf8f9jj7hcki9dk68ao8ietv@google.com RECURRENCE-ID;TZID=America/New_York:20220310T140000 CREATED:20220128T223503Z DESCRIPTION:This observation is unexpected in the momentum -relaxing picture of transport\, but finds a natural explanation in the hyd rodynamic picture where collisions among electrons conserve momentum. In no rmal-state liquid 3He\, both viscosity and thermal diffusivity decrease upo n warming and momentum-conserving collisions among fermions produces a T-sq uare thermal resistivity. Our results imply that the presence of this effec t in ultraclean metals. \;
Since the Wiedemann-Franz law is recovered when collisions by defects outweigh momentum-conserving colli sions\, \; T-square electrical resistivity can arise in absence of Umkl app events in a ‘dirty’ metal. This would provide a solution to the puzzlin g persistence of T-square resistivity in dilute metals such as doped stront ium titanate. \; \;
Host: PaglioneHost: \; Dennis Drew
Title: Creating Hybrid Quantum Technologies with Integ rated Diamond Membranes
Abstract: I n this Colloquium\, I will introduce how we create diamond membranes with u nprecedented quality and integrate them into hybrid quantum and electronic technologies. Diamond has exceptional material properties as a host for qub its yet presents myriad challenges for integration and scalable manufacturi ng. The continued evolution of quantum and electronic technologies in diamo nds requires heterogeneous material platforms for sophisticated functionali ties\, device integration\, packaging\, and improved performance. At UChica go and Argonne National Laboratory\, we are creating pristine single-crysta l diamond membranes that host coherent color center qubits and integrating them with a wide range of materials including silicon\, fused silica\, sapp hire\, thermal oxide\, lithium niobate\, tantalum\, and YIG. The membrane u niformity and robustness to fabrication allow us to create state-of-the-art technologies -such as integrated photonics with record performance\, multi -functional quantum sensing platforms\, and quantum networking interfaces t hat operate at 4 Kelvin instead of resource-intensive dilution fridge tempe ratures. I will also demonstrate how diamond color centers can operate as h igh-performance optical antennas to manipulate and study their proximal env ironment.
Title: Probing Phase Transitions inTopological 2D Mate rials
Van der Waals materials exhibit a rich phase di agram shaped by structural changes and electronic order in both interlayer and intralayer arrangements. An example is twistronics\, where tuning inter layer stacking leads to novel electronic properties. A deeper understanding of phase transitions in 2D materials and their effects on optical and elec trical properties will unlock new opportunities for the development of 2D-m aterial-based devices. In this talk\, I will present experimental studies o n phase transitions in topological 2D materials such as TaIrTe₄ and MoTe₂. First\, I will discuss the nonlinear Hall response as a sensitive probe for mapping the phase diagram of TaIrTe₄ and how this method reveals the relat ionship between structural and topological properties. Second\, I will expl ore the use of nanomechanical resonators to investigate phase transitions b etween different stacking orders.
Host: You Zhou
Refreshments at 1:30 pm - 1117 John S. Toll Bldg
LAST-MODIFIED:20250228T173306Z LOCATION:1410 John S. Toll Bldg SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC Colloquium: Ying Wang\, University of Wisconsin-Madison TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20141009T180000Z DTEND:20141009T190000Z DTSTAMP:20260524T204340Z UID:gjc28mmddphtdt13kjdp81jblk@google.com CREATED:20140813T124827Z DESCRIPTION:Title: Measuring atomic-scale wavefunctions and dynamics inside the hidden order compound URu2Si2 with X-ray spectroscopies\n\nAbstract: U nderstanding the emergent wavefunctions of correlated electron systems requ ires experimental probes that can resolve electronic states on an atomic sc ale. However\, imaging techniques such as STM that resolve single atoms do not provide a good way to distinguish the entangled symmetries of nearby e lectrons. I will talk about how energy-resolved scattering measurements pe rformed with resonance-tuned X-rays can open a unique window into many-body entangled states on an atomic length scale and femtosecond time scale. The presentation will focus on data that unveil entangled wavefunction symmetr ies and energetics of uranium electrons in the "hidden order" compound URu2 Si2\, as well as touching on other material systems of current interest.\n\ nHost: James Williams LAST-MODIFIED:20141003T174553Z LOCATION:Room 1201 Toll Building SEQUENCE:0 STATUS:CONFIRMED SUMMARY:Andrew Wray\, NYU TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20240229T190000Z DTEND:20240229T203000Z DTSTAMP:20260524T204340Z UID:3p2346peaasum5l203i2h1v82d@google.com CREATED:20231110T164210Z DESCRIPTION: Engineering Emergent Correlated States with Complex Quan tum MaterialsLink: \;https://umd.zoom.us/j/91<
/u>251230757?pwd=MkhFREJrUXNTekVZTTRGQ244M1VBZz09<
/b>
Meeting ID: \;912 5123 0757
Password:&nb
sp\; \; 558484
Meeting ID: \;912 5123 0757
Password:&nb sp\; \; 558484 LAST-MODIFIED:20210225T185240Z LOCATION: Online via Zoom SEQUENCE:1 STATUS:CONFIRMED SUMMARY:QMC COLLOQUIUM: Matthew S. Foster\, Rice University TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20171102T140000 DTEND;TZID=America/New_York:20171102T153000 DTSTAMP:20260524T204340Z UID:22r21gjql8i94olaocj1sr2uso@google.com RECURRENCE-ID;TZID=America/New_York:20171102T140000 CREATED:20170424T201551Z DESCRIPTION:SPEAKER: Jak Chakhalian\, Rutgers University\n\nTITLE: Design er Quantum Matter: From ‘ferrolectric’ metal and magnetic 2D electron gas t o quantum spin liquids\n\nABSTRACT: Complex oxides with correlated electron s are a class of materials characterized by multiple competing and nearly d egenerate ground states due to interactions that create a subtle balance to define the lowest energy state. This notion leads to a wide diversity of i ntriguing properties ranging from high Tc superconductivity to exotic magne tism and spin and orbit entangled phenomena. By utilizing the bulk properti es of these materials as a starting point\, interface between different cla sses of correlated oxides combined with geometrical lattice engineering off er a unique opportunity to break the fundamental symmetries of bulk and dev ise novel many-body and topological phases. These designer structures with enhanced electronic correlations\, spin-orbit coupling\, and lattice geomet ries supporting frustrated magnetic interactions can serve as a remarkably fertile ground for unusual quantum states of matter.\n\nUtilizing our recen t advances in complex oxide growth with the atomic layer precision\,\nwe ca n now combine layers of materials with distinct and often antagonistic orde r parameters to create novel artificial quantum materials. The broken latti ce symmetry\, strain\, and altered chemical and electronic environments at the interfaces then provide a unique platform to manipulate this subtle bal ance and enable novel quantum states. Understanding of these phases\, howev er\, requires detailed microscopic studies of the heterostructure propertie s. To illustrate these challenges and opportunities\, I will address the is sues of manipulating magnetic interactions on the nanoscale and understandi ng the behavior of spins in the ultimate2D limit\, modulated carrier densit y\, and orbital polarization. I will demonstrate the examples of realizatio n of a magnetic 2D electron liquid and ‘ferroelectric’ 2D metal. In additio n\, I will discuss our recent efforts towards designer topological material s with QAH and quantum spin liquid states.\n\nHOST: Johnpierre Paglione LAST-MODIFIED:20180420T140559Z SEQUENCE:1 STATUS:CONFIRMED SUMMARY:CNAM Colloquium: Jak Chakhalian\, Rutgers University TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20251016T180000Z DTEND:20251016T193000Z DTSTAMP:20260524T204340Z UID:1to5bu7c1pjeod3jv03i1lh0i8@google.com CREATED:20250825T152217Z DESCRIPTION:Title: Fragile magnetism in metallic transition metal chalcogenides
Abstract: Magnetism in layered van der Waals (vdW) materials provides a remarkable setting to revisit long-standin g concepts in solid-state physics and to explore new pathways for device ap plications. Unlike conventional magnetic thin films\, vdW magnets display e xtraordinary sensitivity to small changes in composition\, stacking\, and d imensionality\, which can dramatically alter their ground states. In this t alk\, I will highlight how subtle modifications - such as minute stoichiome tric changes or magnetic alloying inside the vdW skeleton - can switch magn etism\, stabilize unexpected high-temperature order\, or reshape the low-en ergy flat electronic bands. I will also discuss the role of interlayer inte ractions as a powerful control knob\, underscoring how the fragile magnetis m here reflects the broader theme of tunability in vdW quantum materials. F inally\, I’ll show our recent effort of integrating kGauss level magnetic f ield with ARPES\, paving way for future in situ spectral investigations of metallic magnets.
David Hsieh
California Institute of Techn ology
"Strongly Driven Quantum Materials"
Driving strongly co rrelated electron \;systems far from equilibrium can lead to fundamenta lly new many-body phenomena that are thermally inaccessible. In this talk\, I will describe a series \;of recent experiments that leverage advance d ultrafast optical spectroscopic techniques to uncover transient propertie s of Mott insulators driven by intense electromagnetic fields. By tailoring the characteristics of the electromagnetic field\, I will show how differe nt out-of-equilibrium phenomena can be selectively realized. In particular\ , I will highlight the control of magnetic order using resonant driving\, t he nonlinear production of electron-hole pairs via off-resonant driving\, a nd coherent “Floquet” engineering of electronic band structures and optical properties via far off-resonant driving. \; \;
Title: \; \;Intertwi ned Charge Density Wave Order and Superconductivity in New Classes of Kagom e Metals
Abstract: \;Compounds built from
two-dimensional kagome \;networks of metal ions have long been of inte
rest due to their potential for \;realizing a broad array of anomalous
electronic states\, ranging from quantum \;spin liquid phases to unconv
entional superconductivity. \; More recently\, \;kagome metals have
come into focus as compelling platforms featuring an \;interplay betwe
en topologically nontrivial electronic states and correlated \;electron
phenomena. \; This interplay can naively be realized via the coexisten
ce of an \;interference-driven flat band\, Dirac points\, as well as mu
ltiple van Hove \;singularities formed from the band structure of the k
agome network. An enduring \;challenge is to identify these states in r
eal materials\, and\, in this talk\, I \;will present recent work explo
ring the AV3Sb5
Zoom \;Meeting \;Link: \; \;https://umd.zoom.us/j/91301075848
Refreshme
nts 1:30pm 1117 Toll Physics Bldg.
Spin-valley locking and nonlinear Hall effect in a noncen trosymmetric Dirac material
S pin-valley locking in the band structure of monolayers of MoS2 a nd other group-VI transition metal dichalcogenides (TMDCs) has attracted en ormous interest\, since it offers potential for valleytronic and optoelectr onic applications. Such an exotic electronic state has sparsely been seen i n bulk materials. In this talk\, I will show a bulk spin-valley locked ele ctronic state in a 3D non-centrosymmetric Dirac materialBaMnSb2 [1]. Such a state is revealed by comprehensive studies using first principl es calculations\, tight-binding and effective model analyses\, angle-resolv ed photoemission spectroscopy measurements. Moreover\, this material also e xhibits a stacked quantum Hall effect (QHE). The spin-valley degeneracy ext racted from the QHE is close to 2. This result\, together with the Landau l evel spin splitting\, further confirms the spin-valley locking picture inBa MnSb2. Recently\, we also found such a spin-valley locked state leads to a bulk intrinsic nonlinear Hall effect at room temperature\, which is characterized by alternating current driven second-harmonic and rectifi ed Hall voltage response under time-reversal symmetry conditions [2]. These findings broaden the coupled spin and valley physics in 2D systems into a 3D system. Additionally\, I will also report on a colossal nonreciprocal Ha ll effect caused by an extrinsic nonlinear Hall effect in focused ion depos ited Pt.
References:
[1] Liu et al.\, Nature Commun ications 12\, 4062(2021).
[2] Min et al.\, Nature Communications 14\, 364(2023).
[3] Min et al.\, arXiv:2303.03738.
Refreshments 1:30 pm at 1 117 Toll Physics Bldg.
LAST-MODIFIED:20231106T161913Z LOCATION:Toll Physics Rm 1201 SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC COLLOQUIUM: Zhiqiang Mao\, Penn State TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20250403T180000Z DTEND:20250403T193000Z DTSTAMP:20260524T204340Z UID:6gqbhgi5pusc7pahobies1rfos@google.com CREATED:20250321T135335Z DESCRIPTION:Title: Magnetic field induced superconductivity in two -dimensional crystals
Abstract: In this talk\, I will
discuss the physics of how manipulating magnetic fluctuations can give ris
e to field-induced superconductivity in crystalline two-dimensional quantum
matter. We have explored this effect in high-quality thin films grown via
molecular beam epitaxy\, most extensively in the quasi-two-dimensional comp
ound LaSb2. The field-induced phase emerges in ultra-thin compounds when or
bital repairing effects are mitigated and where tuning the polarization of
fluctuations can dynamically be performed using low temperatures and in-pla
ne magnetic fields. I will provide an overview of the material parameter sp
ace and discuss future research directions using sample design approaches.<
/p>
Host: Sardashti
Refreshments at
1:30 pm - 1117 John S. Toll Bldg
LAST-MODIFIED:20250321T135741Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC Colloquium: Joseph Falson\, Caltech
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20200319T180000Z
DTEND:20200319T190000Z
DTSTAMP:20260524T204340Z
UID:4gh2geqd8fcboirf8p931pmsjg@google.com
CREATED:20191212T191334Z
LAST-MODIFIED:20191212T191334Z
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:NO QMC SEMINAR
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20151001T180000Z
DTEND:20151001T193000Z
DTSTAMP:20260524T204340Z
UID:cneqev3krpotsd2ot1od1j19qc@google.com
CREATED:20150803T144612Z
DESCRIPTION:SPEAKER: Shane Cybart\, UC San Diego\n\nTITLE: Direct-write He
lium Ion Lithography of YBa2Cu3O7 Nano Josephson junctions and SQUIDs \n\nA
BSTRACT: The 1986 discovery of high transition temperature (high-TC) superc
onductivity in copper-oxide materials set in motion an intense research eff
ort to develop superconducting electronics functioning in the range of liqu
id nitrogen temperatures (77 K). Scientists and engineers soon after discov
ered that these materials were much more difficult than initially imagined.
Anisotropic electrical properties and a very short superconducting coheren
ce length seriously narrowed or eliminated the possibility of using existin
g fabrication techniques of conventional superconductors. These new materia
ls demanded novel device architectures that proved very difficult to realiz
e. Nearly three decades have passed and progress in high-TC superconducting
devices has been very slow because process control at the sub ten nanomete
r scale is required to make high-quality\, reproducible Josephson junctions
: the basic building block of superconducting electronics. Recent advances
in gas field focused helium ion beams provide a new and promising approach
for direct-write lithography of high-TC materials for the realization of pr
edictable and scalable high-TC electronics. \nI will describe how my labora
tory uses a 0.5 nm diameter focused helium beam to directly write Josephson
barriers into the a-b plane of a YBa2Cu3O7−δ (YBCO) superconducting thin f
ilm. The key to this method is that YBCO is sensitive to point defects in t
he crystal lattice caused by ion irradiation. Increasing irradiation levels
has the effects of increasing resistivity and reducing the superconducting
transition temperature. At very high irradiation levels YBCO becomes insul
ating and no longer superconducts. The very small size of the barrier creat
ed using a focused helium beam allows us to create junctions with higher ba
rriers than previously possible which allows for insulating barriers and hi
gher resistance devices. I will present data showing how the Josephson barr
ier goes through the metal to insulator transition with increasing irradiat
ion dose\, and discuss a modified restively shunted junction model that des
cribes our data. I will conclude with a discussion about how the helium ion
direct-write method enables for novel experiments in nanoscale Josephson j
unctions and studies of the in-plane anisotropy of the superconducting orde
r parameter symmetry.\n\nHOST: Ben Palmer
LAST-MODIFIED:20150923T185907Z
LOCATION:John S Toll Physics Bldg.\, room 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:CNAM COLLOQUIUM: Shane Cybart\, UC San Diego
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180301T140000
DTEND;TZID=America/New_York:20180301T153000
DTSTAMP:20260524T204340Z
UID:22r21gjql8i94olaocj1sr2uso@google.com
RECURRENCE-ID;TZID=America/New_York:20180301T140000
CREATED:20170424T201551Z
DESCRIPTION:
SPEAKER: Ian Appelbaum\, UMD
TITLE: \; Hidd
en spin polarization?
ABSTRACT: In the presence of time-reversal symmetry\, spin degenera
cy is immune against spin-orbit interaction in centrosymmetric lattices (i.
e. structures that possess inversion symmetry). However\, many such structu
res can be decomposed into complementary but NONcentrosymmetric sublattice
"sectors". Does it make sense to assign a distinct -- and spin-split -- ele
ctronic structure to each one of these coupled components? Recent work usin
g computationally opaque density functional theory\, along with subsequent
experimental analysis using spin-polarized ARPES on layered 2D materials ap
pears to say yes. In this talk\, I will use simple analytic models to argue
for strict caveats to this point of view. \; [https:
//arxiv.org/abs/1801.
Superconductivity in layered nickelates<
br> Harold Y. Hwang \, Department of Applied Physics\, Stanford
University
Unconventional superconductiv
ity in proximity to various strongly correlated electronic phases ha
s been a recurring theme in materials as diverse as heavy fermion co
mpounds\, cuprates\, pnictides\, and twisted bilayer graphene. Here
we will introduce a new and growing family of layered nickelate supe
rconductors. The initial discovery of superconductivity in infinite-
layer nickelates was motivated by looking for an electronic analog o
f the cuprates. Notable aspects are a doping-dependent superc
onducting dome\, strong magnetic fluctuations\, and a landscape of u
nusual normal state properties from which superconductivity emerges.
The subsequent discovery of superconductivity in bulk La3Ni2O7 unde
r high pressure is quite intriguing\, in that the d-electron configu
ration is a priori quite different. Recently\, we have used epitaxia
l strain in (La\,Pr)3Ni2O7 thin films to stabilize superconductivity
at ambient pressure\, which is promising to extend their exp
erimental study and development.
Host: Johnpierre Pa
glione
When: Tuesday\, January 27\, 2026 - 3
:30pm
Where: 1410 Toll Physics Bldg.
RE
FRESHMENTS SERVED AT 3:00pm
Many of th e most interesting and exotic quantum materials are intrinsic superconducto rs o rare induced by proximity to a superconductor. In these materials\, un ique information about their quantum state and excitations can be revealed by measuring their phase-dependent properties. The directionality and phase -sensitivity of the Josephson effect\, the tunneling of Cooper pairs betwee n two superconductors\, provides a powerful probe of the phase anisotropy o f unconventional superconductors and the nature of coherent states in hybri d devices incorporating superconductors and complex materials. In this talk \, I will first review the technique and applications of Josephson interfer ometry. I will describe how this approach\, originally developed to determi ne the order parameter symmetry of the high temperature cup rate supercondu ctors\, is now being used to probe many other exotic superconducting materi als which exhibit multiple superconducting states\, complex order parameter s that breaktime-reversal symmetry\, and topological materials. I will the n describe related schemes for measuring the current-phase relation of Jose phson devices. I will outline how these measurements are being used to stud y supercurrent transport in hybrid devices that reveal phase-modulated elec tronic structure\, explore the interplay of superconductivity and magnetism \, and search for exotic excitations such as Majorana states in topological superconductor devices that could enable topologically-protected quantum c omputing.
Host: Johnpierre Paglione
LAST-MODIFIED:20230131T163521Z SEQUENCE:0 STATUS:CONFIRMED SUMMARY:CARR LECTURE: Dale van Harlingen\, UIUC TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20230126T140000 DTEND;TZID=America/New_York:20230126T153000 DTSTAMP:20260524T204340Z UID:5sqgc92ns31ji7fi7f56lcl20q@google.com RECURRENCE-ID;TZID=America/New_York:20230126T140000 CREATED:20220829T135334Z DESCRIPTION:Title Atomic semiconductor via flat phonon ban ds in HfO2
Abstract: Flatenergy bands in the momentum
space of electrons were known to generate spatiallylocalized states and pro
duce unconventional phenomena such as graphenesuperconductivity. However\,
flat bands in a phonon had not been discovered yet.We were the first to dis
cover that they exist in a ferroelectric HfO2and produce localiz
ed polar displacement of individual atomic layers [1]. Strikingly\,this ato
mic layer is freely displaced by external voltage for the densest informati
onstorage. Our theory of atom control directly in solid [1] is applicable t
o the Si-compatibleHfO2\, so can be materialized in most electro
nic devices reaching upto ~100 TB memories.
\;[1] “Scale-fre eferroelectricity driven by flat phonon bands in HfO2”\, H.-J. L ee etal.\, Science 369\, 1343 (2020).
Metallic kagome lattice materials are emerging as ric h systems for exploring the interplay between topology\, correlation\, and frustrated magnetism. Competing phases and rich phase diagrams are expected in these materials. Here we focus on hexagonal HfFe6Ge6-type“166” compounds\, which are a large family of intermetallics relate d to CoSn. I will discuss magnetism and transport in MMn6Sn 6 (M= Y\,Sc\, and Lu) and also some recent results involving the char ge density wave formed in ScV6Sn6. I will also briefl y discuss recent progress in developing the capability to perform neutron d iffraction under applied electrical current at the Spallation Neutron Sourc e as well as an exciting new family of materials in which magnetic moments can be induced by electrical currents.
Host: Paglione\;[1] \;Gen Yin\, Yufan Li\, Lingyao Kong\, R oger K. Lake\, C.L. Chien\, and Jiadong Zang \;Phys. Rev. B \;93\, 174403
[2] Jie-Xiang Yu\, Jiadong Zang\, Roger K Lake\, Yi Zhang\, an dGen Yin\, arXiv:2106.09073
Convergent Strategies for Design and Characterization of
Low-Dimensional Quantum Materials
Dr. Daniel J. Ri zzo\, Department of Physics\, Columbia University
Abstract : Low-dimensional materials are ideal test-beds for studying fundamenta l solid-state physics and hold significant promise as future platforms for technological advancement. Recent advances in both bottom-up and top-down f abrication techniques have enabled piecewise modification of crystal struct ure and composition\, generating a pantheon of new experimentally accessibl e nanomaterials. At the same time\, the ability to tailor emergent behavior at the atomic-scale requires precise knowledge of structure-function relat ionships using high resolution spatial imaging techniques. In this talk\, I will highlight our recent successes in directing novel electronic\, magnet ic\, optical and plasmonic behavior in 0D\, 1D\, and 2D materials using a f amily of techniques based on both atomic force microscopy and scanning tunn eling microscopy (individually and in consort). Focusing on high watermarks from my own research career\, I will discuss how convergent fabrication an d characterization techniques have laid the groundwork for the next generat ion of low-dimensional quantum materials.
In-Person Location: Toll Ph
ysics Room # 1201
Time: 4pm -5:00pm
Also on Zoom:
Meeting Link - https://umd.zoom.us/j/97540478019
Refreshments 3:30pm 1117 Toll Physics Bldg.
LAST-MODIFIED:20230301T144329Z LOCATION:Toll Physics Room # 1201 SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC SEMINAR: Daniel Rizzo\, Columbia TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20240502T180000Z DTEND:20240502T193000Z DTSTAMP:20260524T204340Z UID:0a67tubobqg5n749kilgtunc76@google.com CREATED:20231110T151545Z DESCRIPTION:OBSERVATION OF FRACTIONAL QUANTUM ANOMALOUS HALL EFFECT< br>Seminar also on Zoom
\, \;Meeting \;Link: \; \;https://umd.zoom.us/j/91301075848
Refreshments 1:30pm 1117 Toll Physics Bldg.
Towards an efficientfirst-principles theory of str ongly correlated electron materials
F
irst\, we introduce a new variational approach to the quantum many-body pro
blem: the variational discrete action theory (VDAT). VDAT introduces an ans
atz for the many-body wave function which is controlled by an integer N\, w
here N = 1 recovers Hartree-Fock\, N = 2 recovers the Gutzwiller wave funct
ion\, and increasing N monotonically approaches the exact solution. The key
breakthrough of VDAT is that this wave function ansatz can be exactly eval
uated in infinite dimensions with a finite number of operations. In the con
text of the multi-orbital Hubbard model\, a minimal model of SCEM\, we will
showcase results that demonstrate VDAT at N = 3 has a computational cost c
omparable to the Gutzwiller approximation while recovering Mott and Hundphy
sics with remarkable accuracy.
The second development we present is
the irreducible derivative approach to computing phonons and their interact
ions\, which is the most efficient finite difference approach allowed by gr
oup theory. Phonons and their interactions are necessary for untangling the
vibrational component of any observable\, which is essential for understan
ding SCEM. Given that linear response is impractical for most beyond DFT me
thods\, it is critical to pioneer the best possible finite difference metho
d. We showcase the irreducible derivative method by computing phonons\, pho
non interactions\,the interacting phonon Green’s function\, and thermal con
ductivity in a variety of materials\, including the Mott insulator uranium
dioxide.
Host: Paglione/Butch
Refreshments a
t 1:30 pm - 1117 John S. Toll Bldg
VdW heterostructures: a new route to quantum matte r
From superconductivity to fractionalized particl es\, fascinating phenomena arise in quantum materials due to the collective behaviors of electrons. These quantum phenomena are not only captivating f or physicists\, but they also offer significant opportunities for future qu antum technologies. In my talk\, I will introduce van der Waals (vdW) heter ostructures as a rising platform to fabricate new quantum materials. These heterostructures are made by mechanically assembling layers of two-dimensio nal materials together\, breaking through traditional material synthesis li mitations and providing new ways to create quantum matter.
Du ring the first part of my talk\, I will demonstrate how the interplay betwe en different atomic layers can be leveraged to design unique quantum proper ties. Specifically\, I will focus on graphene double-layers\, where interla yer Coulomb interactions are exploited to enable a superfluid condensate of fermion pairs with an adjustable coupling strength. This realization helps us achieve a long-sought paradigm known as BEC-BCS crossover. In the secon d part\, I will discuss our efforts to develop scanning tunneling microscop y (STM)measurements on vdW heterostructures\, enabling us to uncover hidden quantum properties and decipher enigmatic quantum states of matter. I will use our experiments on visualizing quantum Hall states in graphene to show case our capabilities and the power of the local probe. Finally\, I will co nclude by sharing my vision for exploring major themes in condensed matter physics through the flexible integration of different interplays between se parate atomic layers and by extending our state-of-the-art STM measurements to a wide range of vdW devices.
T he functionality of solid-state devices is often linked to phase transition s in one or more of the components. In order to optimize the properties of these solid state materials\, it is important to understand how the propert ies emerge from the fundamental electronic interactions. Vanadium dioxide ( VO2) is famous for its metal-to-insulator phase transition slightly above r oom temperature\, which includes a strong structural component. The nature of the structural instability within the transition is not fully understood \, let alone whether it is a result or the cause of the electronic transiti on. Moreover\, chemical substitution leads to unexpected changes in the str ucture and properties\, indicating a complex balance of interactions underl ying the transition. This seminar will present state-of-the-art total x-ray scattering measurements on VO2 alloyed with other transition metals that r eveals a new and unique phase at low temperatures\, dubbed the “2D-M2 phase ”\, that is characterized by ordering of atomic displacements in only two d imensions. The structural details of the 2D-M2 phase are explained by a geo metric frustration model\, where ordering along one axis impedes ordering o n its symmetry-equivalent partner. These findings suggest that previous ele ctronic models that could not predict this behavior are likely incomplete. Comparing the physical properties systematically across multiple compositio ns suggest that electron-correlations are important to the phase transition . \;
Related Publications
Davenport\, Mathe w A.\; Allred\, J.M.\; A crystallographic approach to the short-range order ing problem in V1-xMoxO2 (0.50 ≤ x ≤ 0.60)\, J. Mater. Chem. C\, 8\, 10907- 10916\, (2020) DOI: 10.1039/D0 TC01173H
Davenport\, Matthew A.\, Confer\, Matthew P\, D ouglas\, Tyra C\, Rawot Chhetri\, Top B.\, Allred\, Jared M.\; Large single crystals of V1-xMoxO2 from a two-step\, chemical vapor transport synthesis . Cryst. Growth Des.\, 20\, 6\, 2625-2640 (2020) DOI: 10.1021/acs.cgd.9b01296
Dav enport\, M. A.\, Krogstad\, M. J.\; Whitt\, L. M.\; Hu\, C.\; Douglas\, T.C . Douglas\; Ni\, N.\; Rosenkranz\, S\; Osborn\, R.\; Allred\, J. M.\; Fragi le 3D Order in V1-xMoxO2. Under Review\, Submitted November 2019\; Accessib le as a pre-print on arXiv:1909. 12704 \;
Meeting ID: \;912 5123 0757
Password: \; \; 558484 LAST-MODIFIED:20210225T161650Z LOCATION: Online via Zoom SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC COLLOQUIUM: Jared Allred\, University of Alabama TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20141106T190000Z DTEND:20141106T200000Z DTSTAMP:20260524T204340Z UID:rrrgcdbb4ejduh41rue4clumv0@google.com CREATED:20140813T124932Z DESCRIPTION:SPEAKER: David Hsieh\, CalTech\n\nTITLE: Search for novel qua ntum phases in 5d transition metal oxides using nonlinear optics\n\n\nABSTR ACT: Recently there is growing interest to understand whether fundamentall y new quantum phases can emerge when strong electron correlations and spin- orbit coupling occur on comparable energy scales in the same material. Rapi d advances in the synthesis of 5d transition metal oxides now present an un precedented opportunity to experimentally address the physics of this uniqu e parameter regime. \nIn this talk\, I will focus on the perovskite irida te Sr2IrO4\, which has been studied particularly intensively due to its nov el Jeff = ½ magnetic Mott insulating ground state and potential for high-Tc superconductivity upon doping. I will describe how nonlinear optical spect roscopy and microscopy measurements have the unique capability to determine the symmetries of both its lattice and electronically ordered phases and s patially resolve their domain distribution. I will discuss our recent resul ts that explain the perfect magneto-elastic locking in Sr2IrO4 and our obse rvation of a strange hidden phase that has until now eluded other probes. \ n\nHOST: James Williams\n LAST-MODIFIED:20141030T161149Z LOCATION:Room 1201\, Physics Toll Building SEQUENCE:0 STATUS:CONFIRMED SUMMARY:David Hsieh\, CalTech TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20150205T140000 DTEND;TZID=America/New_York:20150205T153000 RRULE:FREQ=WEEKLY;UNTIL=20150507T180000Z;BYDAY=TH DTSTAMP:20260524T204340Z UID:q985v6uteua502t37rg0nfh3ok@google.com CREATED:20150115T203357Z DESCRIPTION:SPEAKER: Prof. Brian Leroy\, Arizona\n\nTITLE & ABSTRACT TBD LAST-MODIFIED:20150118T224200Z LOCATION:Phys. Rm 1201 SEQUENCE:1 STATUS:CONFIRMED SUMMARY:CNAM Condensed Matter Colloquium TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20170126T140000 DTEND;TZID=America/New_York:20170126T153000 RRULE:FREQ=WEEKLY;UNTIL=20170511T180000Z;BYDAY=TH EXDATE;TZID=America/New_York:20170316T140000 EXDATE;TZID=America/New_York:20170323T140000 DTSTAMP:20260524T204340Z UID:ua8bnb6fr09o4ste1b9vrnc0e8@google.com CREATED:20160624T143638Z DESCRIPTION:SPEAKER\, TITLE & ABSTRACT: TBD LAST-MODIFIED:20170203T151543Z LOCATION:Rm 1201 John S Toll Physics Bldg SEQUENCE:0 STATUS:CONFIRMED SUMMARY:CNAM COLLOQUIUM TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20180205T210000Z DTEND:20180205T220000Z DTSTAMP:20260524T204340Z UID:49dkf8b0k4156e369ts7lhklkj@google.com CREATED:20171212T010030Z DESCRIPTION:\n\nSPEAKER: Robert Schoelkopf\, Yale University\n\nTITLE: Sc hrodinger’s Catapult: Quantum Communication with Microwave Photons\n\nABSTR ACT: An important ability for quantum communication networks or for scalab le quantum computers is the ability to robustly convey quantum information between separable elements\, and generate entanglement on demand. We have r ecently demonstrated the ability to generate and launch single microwave ph otons through a coaxial cable. Moreover\, this can be extended to more comp lex non-classical states with multiple photons\, including small cat states \, hence the term “Schrodinger’s catapult.” I will show experiments in whic h we can\nconvert from standing states in a cavity to flying photons in a t ransmission line\, and the ability to make and measure entanglement between standing and flying states. Furthermore\, we can use these techniques to t ransfer an encoded bit of quantum information between two modules that are separated by a meter of coaxial cable. Finally\, one can perform a “half-tr ansfer to generate remote entanglement on demand. I will also discuss the p rospects for applying quantum error correction techniques to compensate for the small but inevitable losses during the transmission process. LAST-MODIFIED:20180201T210927Z LOCATION:Room 1201 Toll Bldg.\; Refreshments at 3:30 in room 1117 Toll Bldg . SEQUENCE:0 STATUS:CONFIRMED SUMMARY:Special Seminar: Dr. Rob Schoelkopf\, Yale TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20141002T180000Z DTEND:20141002T190000Z DTSTAMP:20260524T204340Z UID:vp9rnkmv6u0s8qb901iuipc26s@google.com CREATED:20140813T124811Z DESCRIPTION:Vidya Madhavan\, University of Illinois\, Urbana-Champaign\n\nT itle: Symmetry Protected Dirac Fermions in Topological Crystalline Insulato rs\n\nAbstract: In Dirac materials like graphene and topological insulators \, electrons behave like relativistic particles with no mass. This is a dir ect consequence of the form of the low-energy Hamiltonian describing these electrons and has important implications for realizing physical properties predicted for high-energy particles\, now in the laboratory setting. Topolo igcal crystalline insulators are recently discovered topological materials [1\,2] where topology and crystal symmetry intertwine to create relativisti c massless electrons. Among the theoretical predictions for topological cry stalline insulators is the possibility of imparting mass to these massless Dirac fermions by breaking symmetry. In this talk I will discuss our recent experimental and theoretical investigations of a topological crystalline i nsulator\, Pb(1-x)Sn(x)Se [3\,4]. We perform scanning tunneling microscopy (STM) studies at low temperatures and as a function of magnetic field. By a nalyzing two types of STM data: Fourier transforms of interference patterns and Landau level spectroscopy\, we reveal the coexistence of zero mass Dir ac fermions protected by crystal symmetry with massive Dirac fermions resul ting from crystal symmetry breaking. In addition\, I will discuss our recen t data on the evolution of the mass as well as the Dirac surface state as w e go through a quantum phase transition from the topological to trivial reg ime [5]. Finally as time permits\, I will discuss our new data on thin film s of topological crystalline insulators where we directly measure the effec ts of strain on the topological surface states.\n\n[1] L. Fu. Phys. Rev. Le tt. 106\, 106802 (2011).\n[2] T. H. Hseih et al.\, Nat. Commun. 3\, 982 (20 12).\n[3] Y. Okada et al.\, Science 341\, 1496 (2013).\n[4] I. Zeljkovic et al.\, Nat. Phys. 10\, 572 (2014).\n[5] I. Zeljkovic et al.\, arXiv:1403.49 06 (2014). LAST-MODIFIED:20141001T142223Z LOCATION:Room 1201 Toll Bldg SEQUENCE:0 STATUS:CONFIRMED SUMMARY:Vidya Madhavan\, University of Illinois\, Urbana-Champaign TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20180419T140000 DTEND;TZID=America/New_York:20180419T153000 DTSTAMP:20260524T204340Z UID:22r21gjql8i94olaocj1sr2uso@google.com RECURRENCE-ID;TZID=America/New_York:20180419T140000 CREATED:20170424T201551Z DESCRIPTION:Abstract: \; While there hasbeen tremendous recent progress in the realization of small-scale quantumcircui ts comprising of order 10 qubits\, research indicates that afault-tolerant quantum computer that exceeds what is possible on existingclassical machine s will require a network of thousands or millions of qubits\,far beyond cur rent capabilities. Robust approaches to the measurement andcontrol of large -scale next-generation quantum processors have yet to bedeveloped.
In this talk I describean experimental program to develop high-f idelity qubit measurement and controlcircuitry based on the superconducting Single Flux Quantum (SFQ) digital logicfamily. Qubit measurement is perfor med by mapping the state to the microwavephoton occupation of a linear reso nator followed by subsequent photodetectionwith a microwave photon counter. This scheme provides access to the binarydigital output of qubit measureme nt at the millikelvin experimental stage\,without the need for room-tempera ture heterodyne measurement and thresholding. Rawsingle-shot measurement fi delity up to 92% has been achieved\, limited by qubitrelaxation. Moreover\, we exploit the intrinsic damping of the counter to efficientlyextract the energy released by the measurement process\, allowing fast\, repeatedhigh-f idelity measurements.
Coherent controlof the qub it is performed using trains of quantized SFQ flux pulses. Each ofthese pul ses provides a delta function-like kick to the qubit\, inducing atrajectory on the Bloch sphere that can be tailored to minimize leakage errors.We des cribe the fabrication and characterization of a transmon qubit chip incorpo ratingan on-chip SFQ pulse driver. We achieve gate fidelity up to around 98 %\, limitedby quasiparticle generation from the dissipative SFQ pulse drive r. I discussnext-generation designs that are expected to significantly miti gatequasiparticle poisoning.
These two effortspoi nt a direction toward the integration of a large-scale superconductingquant um processor with proximal classical superconducting logic for thepurposes of reducing latency\, wiring heat load\, and overall system footprint.
Host: Vladimir Manucharyan LAST-MODIFIED:20180420T140559Z LOCATION:Rm 1201 John S Toll Bldg SEQUENCE:1 STATUS:CONFIRMED SUMMARY:CNAM Colloquium: Robert McDermott\, Univ of Wisc TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20231109T190000Z DTEND:20231109T203000Z DTSTAMP:20260524T204340Z UID:31in2kfcp8bim5tvqmu2h52ovg@google.com CREATED:20230821T180045Z DESCRIPTION:All-electronic detection of DNA oli gomers holds promise for significantly advancing biotechnology. However\, k nown all-electronic methods rely solely on measuring electrical signals of transducers during DNA hybridization. As a result\, these methods are susce ptible to nonspecific electrostatic and electrochemical interactions\, whic h limit their detection specificity and sensitivity. We develop a nanomecha noelectrical approach with exceptional specificity and a100-fold improvemen t in detection limit. In this approach\, DNA strands tethered to a graphene transistor are driven to oscillate in an alternating electric field. We de monstrate that the transistor-current spectrum is characteristic to DNA hyb ridization. We find that the spectral characteristics arise from the differ ence in flexibility between unpaired and paired DNA strands. This transduct ion principle minimizes the influence of nonspecific interactions\, thereby enhancing selectivity and sensitivity. Our method paves the way to high-pe rformance DNA analysis in miniaturized all-electronic systems.
Link: \;https://umd.zoom.us/j/91251230757?pwd=MkhFREJrUXNTekVZTTRGQ244M1VBZz09
Meeting ID: \;912 5123 0757
Password:
\; \; 558484
Select quantum mat erials can support polaritons: hybrid light-matter waves with subdiffractio nal confinement. Infrared nano-imaging can be used to detect these polarito nic waves\, yielding insights into the properties of the host materials. In this talk\, I will discuss polaritons in several hyperbolic materials\, wh ich propagate as conical rays throughout the bulk of these crystals. We det ected hyperbolic exciton-polaritons in the van der Waals semiconductor WSe< sub>2 in a light-induced state. Our time-resolved nano-imaging data r evealed key signatures of transient optical hyperbolicity [1]. I will also introduce polaritons in hyperbolic hetero-bicrystals. We observed negative refraction\, spectral gaps\, and polariton wave localization in a hetero-bi crystal made of the two thin crystals: Molybdenum oxide and isotopically pu re hexagonal boron nitride. I will overview signatures of strong polariton- polariton coupling\, which are evident in the hetero-bicrystal dispersion [ 2]. Some of the challenges and opportunities for polaritons in quantum mate rials will be discussed.
[1] A. J. Sternbach et al.\, Scie nce 371\, 617 (2021)
[2] A. J. Sternbach\, et al.\, Science 379\, 555 (2023)
Building the Next Generation of Spin Qubits
Quantum computers have the potential to be a tran
sformative technology. While there are many possible platforms for developi
ng a viable quantum computer\, spin qubits offer several unique advantages\
, such as their potential for scaling using established semiconductor manuf
acturing techniques. However\, they face a number of challenges\, largely s
temming from their sensitivity to the environment. In this talk\, I will di
scuss my research on combating this sensitivity by increasing coherence tim
es and enabling long-distance coupling in spin qubits. I will then present
two projects in which the development of novel materials and devices enable
d the discovery of new physics and functionalities\; first\, a study of unc
onventional superconductivity in infinite-layer nickelate and second\, an i
nvestigation of sources of decoherence in superconductingqubits. These proj
ects demonstrate how active control of material heterostructures can be lev
eraged to design systems with desired traits. I will show how such an appro
ach can be fruitful for the study of spin qubits\, allowing fine control of
their properties and leading to improved quantum devices to implement more
complex quantum architectures.
R efreshments 1:30 pm at 1117 Toll Physics Bldg.
LAST-MODIFIED:20240212T185708Z LOCATION:1201 John S. Toll Building SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC Colloquium: Shannon Harvey\, Stanford University TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20250925T180000Z DTEND:20250925T193000Z DTSTAMP:20260524T204340Z UID:7ospide9rf2as5fuf7hdaoedb1@google.com CREATED:20250827T192354Z DESCRIPTION:Quantum complexity in simple materials
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/b>
Two-dimensional(2D) materials have received widespread attention over the past 20 years due to their remarkable physical\, mechanical\, and chemical properties\, and our ability to integrate them into devices. In th is seminar\, I will discuss a new approach for realizing long-sought electr onic structures of geometrically frustrated lattice models (e.g.\, k agome and pyrochlore)\, by “decorating”un-frustrated\, primitive lattices w ith a particular set of atomic orbitals. In the process\, we identify the v dW intermetallic compound Pd5AlI2as the first materia l to realize the electronic structure of the 2D Lieb lattice– featuring Dir ac-like bands intersected by a flat band – persisting in ambient conditions down to the monolayer limit. I will discuss how this unique electronic str ucture gives rise to compact localized states and bound states in continuum (BICs)\, which could provide a platform for lossless and topologically pro tected electronic processes. I will then detail our recent synthesis of CeS iI\, the first van der Waals (vdW) metal with a heavy fermion ground state. Conceptually\, our synthetic design takes a traditional 3D intermetallic s tructure and slices it into atomically-thin vdW sheets by incorporating iod ine into the structure. The resulting material is cleavable and effectively electronically 2D.
The two-dimensionalkagome lattice model— aside from playing a central part in the context ofmagnetic frustration—has long provided a fruitful theoretical ground for the studyof topological an d correlated electronic phases\, thanks to its peculiar bandfeatures includ ing Dirac fermions and a dispersionless flat band. In recentyears\, a growi ng family of transition element-based intermetallic compoundstermed “kagome metals” are experimentally identified to realize these characteristickagom e band features. Here I will introduce our efforts to search for flatbands in the vicinity of the Fermi level in kagome metals based particularly onla te 3d transition elements (Fe\, Co\, Ni) [1-3]. I will discuss the implicat ionof these flat bands on magnetism and highlight the essential role of d-o rbitaldegrees of freedom therein—insights from which we anticipate to be ap plicableto designing flat bands in broader classes of crystalline materials .
[1]M. Kang\, LY et al.\, Dirac fermions and flat bands in the ideal kagome metalFeSn\, Nat. Mater. 19\, 163-169 (2019).
[2]M. Kang et al .\, Topological flat bands in the frustrated kagome lattice CoSn\,Nat. Comm un. 11\, 4004 (2020).
[3]LY et al.\, A flat band-induced correlated k agome metal\, arXiv/2106.10824
Iron-ba sed Superconductivity\, Multi-orbital Correlations and The Tale of d+d Pair ing
Strongly correlated electron systems often show bad-meta l behavior\, as operationally specified in terms of a resistivity at room t emperature that reaches or exceeds the Mott-Ioffe-Regel limit. Iron-based s uperconductors present a striking case study. Their bad metallicity implica tes orbital-selective electron correlations and\, at the same time\, leads to short-range frustrated spin-exchange interactions. These features\, in t urn\, have important consequences for the superconducting pairing. One is a quasi-degeneracy in various pairing channels\, and another is the emergenc e of the so-called orbital-selective pairing [1]. These issues will be intr oduced in the talk. I’ll then go on to present a unusual pairing state dubb ed “d+d” pairing [2\,3]\, and describe how its matrix structure in the orbi tal space has a surprising formal analogue with its spin-space counterpart in the B-phase of the 3He superfluid [2]. I’ll make the case that the d+d s tate describes certain iron-selenide superconductors (that are among the gr oup of highest Tc iron-based superconductors). In a twist befitting the asp ired universal understanding across strongly correlated superconductors\, t he d+d pairing state turns out [2] to also solve a serious new riddle that recently arose in the heavy fermion system CeCu2Si2\, the very first unconv entional superconductor ever discovered.
[1] Q. Si\, R. Yu and E. Abrahams\, Nature Reviews Materials 1\, 16017 (2016).
[2] E. M. Nica and Q. Si\, Npj Quantum Materials 6\, 3 (2021).
[3] E. M. Nica\, R. Yu\, and Q. Si\, Npj Quantum Materials 2\, 24 (2 017)
Link: \;https://umd.zoom
.us/j/91251230757?pwd=MkhFREJrUXNTekVZTTRGQ244M
1VBZz09
Meeting ID: \;912 5123 0757
Password: \; \; 558484
As Moore’s Law grinds to a halt\, we are entering a new world of software driven hardware\, of ASICs and machin e learning accelerators. This has opened up new opportunities for novel low -power electronics and emerging materials underpinning them. While quantum computing can end up being disruptive in algorithmic scale-up\, there are m any opportunities for classical computing with quantum states based on pres ent day technology that can be quite disruptive as well. There are two exam ples I will focus on – one is doing conventional Boolean logic at low power below the thermal Boltzmann limit\, using the topological properties of Di rac fermions to control transmission across a gated interface. The other is doing collective computing using temporal state machines to solve certain graph theory problems efficiently. An example is skyrmions driven along rac etracks\, whose quasi-linear operation and topologically stabilized lifetim es at ultra-small sizes
can potentially function as tem poral memory in race logic for rapid pattern matching and intermittent-sens or processing applications. These two concepts – topology driven lifetime a nd topology driven transmission\, can be used to accomplish entirely differ ent goals in low-power computing.
Meeting ID: \;912
5123 0757
Imaging Heterogeneity in 2DMaterials with Photoemission E lectron Microscopy
Two-dimensional (2D) materials have taken a central role in condensed matter research and next- generation device design due to their compact size\, turnability\, and nove l electronic properties. Heterogeneity and anisotropy in these materials ar e particularly important as micro- and nano-scale interfaces host emergent phenomena and give rise to new functionalities. In this talk\, I will prese nt our work investigating these types of structures with photoemission elec tron microscopy(PEEM). I will first discuss our results mapping the antifer roelectric domain structure in β′-In2Se3. Although th e antiferroelectric order means that this material contains net-zero sponta neous polarization\, domains remain dichroic\, enabling their imaging with optical probes. With polarization-dependentPEEM\, we interrogate the domain structure with nano-scale precision\, makequantitative domain orientation assignments\, and connect the atomic distortionsto the optically addressabl e mesoscale structure. Avenues for modifying domain arrangements and genera ting multiphase heterostructures will also be explored. Finally\, I will al so discuss our recent investigations of coherent light-matter interactions with PEEM. MoOCl2 is a highly anisotropic 2D material that hosts in-plane hyperbolic plasmon polaritons in the visible range. Spatiotempora l analysis of these modes will be presented in which we visualize their rea l-time propagation and hyperbolic focusing.
Title: \;Magnetism in Moiré Superlattices
Abstract: Moiré superlattices of 2Dmaterials is an emerging platform for studying new physical phenomena with high tuna blity. In this talk\, I will present emergent magnetic interactions in two distinct types of moiré superlattices. I will firstly present the observati on of magnetic textures in small angle twisted 2D magnet chromium triiodide (CrI3).Employing single-spin quantum magnetometry\, we directly visualize nanoscale magnetic domains and periodic patterns\, a signature of moiré mag netism\, and gain quantitative information on domain size and magnetization . The observed AFM and FM domains with periodic patterns are in good agreem ent with the calculated spatial magnetic structures arising from the local stacking-dependent interlayer exchange interactions in CrI3 moiré superlatt ices. Then I will present the drastic tuning of spin-spin exchange interact ions in WSe2/WS2 moiré superlattices by optical excitation\, which results in ferromagnetic order over a small range of doping at elevated temperature s. This discovery adds a new and dynamic tuning knob to the rich many-body Hamiltonian of moiré quantum matter.
Title: Disorder in topologicalsemimetals: insight s from epitaxy \;
Abstract: Topological semimetals\,characterized by linear band touching nodes near the Fermi level\, exhibit remarkableban d structure and transport phenomena. While such phenomena have largely been discovered and studied in bulk crystals\, epitaxial layers will ultimately be requiredto realize devices. We must therefore understand and control the impact ofdisorder occurring in epitaxial material\, including point and ex tended defectsand interfaces. In this talk\, I will discuss our work to thi s end in theprototypical Dirac semimetal Cd3As2. Draw ing on decadesof collective knowledge of disorder regulation in conventiona l semiconductors\,we use molecular beam epitaxy on zinc blende substrates t o select thecrystallographic orientation of the epilayer\, systematically v ary point defectpopulations and synthesize alloys. These factors offer rout es to tune theelectron concentration and mobility and allow us to probe how defects impact magnetotransport behavior. I will also discuss the implemen tation of doubleheterostructures to enable new vertical photodetector desig ns and other futuredevices.
Design and discovery of new quantum materials will accelerate the development of n ew technologies in the future. I will report my group research progress in the past 4 years\, mainly focusing on the new superconductors and new magne tic topological quantum materials. My group recently discovered several new superconductors. I will explain our interpretation of this work. More impo rtantly\, we are trying to use chemical bonding concept to predict the exis tence of superconductivity in the materials. Magnetic topological quantum m aterials (MTQMs) can give rise to forefront electronic properties such as t he quantum anomalous Hall effect\, axion electrodynamics and Majorana fermi ons. In our group\, we used chemistry electron count rules and structure-pr operty relationship to design new MTQMs. I will describe how to design and prove the material candidate as a new MTQM from both experimental and theor etical aspects and show how topological electronic states and magnetism int erplay in the new material. \; \;
Relevant papers:
1. Gui\, X.\, Klein\, R.A.\, Brown\, C.M.\, Xie\, W. “Chemical Bonding Governs Complex Magnetism in MnPt5P” Inorg. Chem. 2021\, 60(1)\, 87-96.&nbs p\;
2. Gui\, X.\, Chang\, T.R.\, Wei\, K.\, Daum\, M.J.\, Graf\, D.E. \, Baumbach\, R.E.\, Mourigal\, M.\, Xie\, W. “A Novel Magnetic Material by Design: Observation of Yb3+ with Spin-1/2 in YbxPt5P.” ACS Central Science \, 2020\, 6(11)\, 2023-2030.
3. Gui\, X.\, Xie\, W. “Crystal Structur e\, Magnetism\, and Electronic Properties of a Rare-Earth-Free Ferromagnet: MnPt5As.” Chem. Mater. 2020\, 32(9)\, 3922-3929.
4. Gui\, X. et. al. “A New Magnetic Topological Quantum Material Candidate by Design.” ACS Cen tral Science\, 2019\, 5(5)\, 900-910.
5. Gui\, X.\, Sobczak\, Z.\, Ch ang\, T.R.\, Xu\, X.\, Huang\, A.\, Jia\, S.\, Jeng\, H.T.\, Klimczuk\, T.\ , Xie\, W. “Superconducting SrSnP with Strong Sn–P Antibonding Interaction: Is the Sn Atom Single or Mixed Valent?” Chem. Mater. 2018\, 30(17)\, 6005- 6013.
6. Xie\, W.\, Luo\, H.\, Phelan\, B.F.\, Klimczuk\, T.\, Cevall os\, F.A.\, Cava\, R.J. “Endohedral gallide cluster superconductors and sup erconductivity in ReGa5.” PNAS\, 2015\, 112(51)\, E7048-E7054.
Link: \;https://umd.zoom.us/j/<
/u>91251230757?pwd=MkhFREJrUXNTekVZTTRGQ244M1VBZz09
Meeting ID: \;912 5123 0757
Passwor
d: \; \; 558484
Emerging Opportunities in 2D Ferroic and Multiferroic Materials and Devices
Two-dimensional(2D) layered van der Waals (vdW) ferroics (e.g.\, ferromagnets [1\,2] and ferroelectrics [3]) are atomic-thin crystalline flatlands with long-range ferroic order. Given that these functional materials are optically transparent\, mechanica lly flexible\, and electrically tunable\, their properties are highly tailo rable by external stimuli\, leading to numerous new physical phenomena and novel device functionalities. In this talk\, I will discuss our series of w orkon optical [4]\, mechanical [5\,6]\, and electrical control of 2D magnet s [7-10]\, with a broad portfolio of condensed matter physics topics studie d\, including spin-photon interaction\, magnetoelastic effect\, and interfe rroic magnetoelectric coupling\, to name a few. Next\, I will explain a uni que set of high-performance vdW ferroelectric tunnel junctions we have deve loped in recent years. Finally\, I will end the talk with a brief introduct ion to our 2D sensors for food safety guarding\, early diagnosis of disease \, and electromagnetic field detection. Hopefully\, the audience will be co nvinced that 2D ferroic and multiferroic materials and devices constitute l argely uncharted territories\, with a wide range of exotic quantum material physics and new device concepts emerging.
1. C.Gong et al. Nature 546\, 265–269 (2017).
2. C.Gong\, X. Zhang. Science 363\, eaav4450 (2019).
3. Q.Wang\, et al. Matter 5\, 4425-4436 (2022).
4. T.Xie\, et al. Nature Physics 21\, 1118–1124 (2025).
5. T.Xie et al. unpublished.
6. Y.Wang et al. unpublished.
7. C.Gong\, et al. Nature Communica tions 10\, 2657 (2019).
8. S.Liang\, et al. Nature Electro nics 6\, 199–205 (2023).
9. S.Liang\, et al. Nature Electr onics 9\, 23–32 (2026).
10. T.Xie\, et al. Nature Nano technology (DOI: 10.1038/s41565-025-02065-1\,2026).
Host: Paglione
Topological Superconductivity\, Majorana Zero Modes and Q uantum Algorithms in Magnet-Superconductor Hybrid Systems
Magnet-Superconductor Hybrid (MSH) systems have proven to be
versatile platforms for the engineering of topological superconductivity a
nd the ensuing Majorana zero modes\, an important step towards the realizat
ion of topological quantum computing. In particular\, the experimental abil
ity to create MSH system with widely varying magnetic structures -- from fe
rromagnetic and skyrmion-like to antiferromagnetic – provided an unpreceden
ted opportunity to manipulate and explore topological phases. In this talk\
, I will review some recent progress in the theoretical prediction and expe
rimental realization of novel topological superconducting phases – ranging
from strong and higher order topological superconductors to topological nod
al-point superconductivity -- in MSH systems. Moreover\, I will demonstrate
how the manipulation of the magnetic structure in MSH systems provides a n
ew path to braiding MZMs and to the real time simulation of topologically p
rotected quantum algorithms
Non-equilibrium control of structure and functional ity in quantum materials with light
Ankit Disa
Max Planck-NYC Center forNon-Equilibrium Quan
tum Phenomena\, New York\, USA/Hamburg\, Germany
\ ;Quantum materials exhibit unique macroscopic phenomena withenormous techno logical potential\, ranging from high-temperaturesuperconductivity to topol ogically protected transport. Hence\, at the forefrontof condensed matter r esearch is the goal of understanding and controlling theiremergent behavior at the smallest length and time scales possible. Due to thestrongly intert wined nature of electrons and the crystal lattice in thesematerials\, manip ulating the atomic structure allows one to tune interactionsand create nove l electronic and magnetic phases. In this talk\, I will describe how light can be used toengineer structural distortions in quantum materials on ultra fast time scales\,providing a powerful pathway to realize non-equilibrium s tates of matter\, oftenwith functionalities not accessible otherwise. First \, I will illustrate theapplication of this approach to the antiferromagnet CoF2. Byresonantly exciting optical phonons at terahertz freque ncies\, a ferrimagneticphase transition can be driven with light\, whose in duced magnetization is100-fold larger than the equilibrium limit. Second\, I will demonstrate that thecoupling of optically driven phonons to long-wav elength strain leads to ametastable ferroelectricity in the quantum paraele ctric SrTiO3. Inthis case\, the symmetry-broken state remains fo r hours after excitation. Theseexperiments provide a basis for the rational design of non-equilibriumfunctionalities. Integrated with targeted materia ls synthesis\, such controlpromises to unlock new physical phenomena and en able next-generation quantumand ultrafast technologies.
Link:
\;https://umd.zoom.us/j/91251230757?pwd=MkhFREJr
UXNTekVZTTRGQ244M1VBZz09
Meeting ID:
\;912 5123 0757
Password: \; \; 558484
\;
Host: Mohammad Hafezi
\;
Phase transitions instigated by an ultrash ort laser pulse usher in a new era for materials engineering in the femto- (10‑15)to pico-second (10‑12 s) regime\, a time windo w that incommensurate with nanoscopic dynamics of electrons\, spins\, and l attice ions. Rapid advances in tabletop ultrafast techniques—such as time-r esolved photoemission\, diffraction\, and core-level absorption—have enable d us to examine complex interactions and out-of-equilibrium states with unp recedented details. In this talk\, I will discuss two important pathways fo r manipulating nonequilibrium phases of matter in quantum materials\, which feature (i) competing orders\, and (ii) strong Coulomb interaction between electrons and holes. More specifically\, an ultrashort light pulse can (i) unleash a hidden order that is suppressed in equilibrium due to phase comp etition\, and (ii) change the dimensionality of an ordered state by modifyi ng excitonic correlations. I will explain the microscopic mechanisms behind these unconventional light-induced states\, highlighting the roles of phot oinduced topological defects\, order parameter fluctuation\, and Coulomb sc reening by excited mobile carriers. These points will be illustrated using examples from materials that exhibit a charge density wave—a spontaneous mo dulation of electron density accompanied by a periodic lattice distortion—w hich serves as a model platform to illustrate general principles underlying ultrafast light-matter interaction in strongly correlated systems.
Title: Probing quantum materials wi th cQED
Abstract: Mesoscopic and low-dimensional materials repr esent one of the frontiers in the study of unconventional superconductivity . Owing to their small size\, these materials are challenging to probe usin g many conventional measurement techniques\, and require new experimental p robes to successfully characterize. In this talk\, we introduce one such pr obe which enables us to measure the superfluid density of micron-size super conductors using microwave techniques drawn from circuit quantum electrodyn amics (cQED).We apply this technique to a well-studied system\, the superco nductor/ferromagnet bilayer\, where we find evidence for anisotropic induce d superconductivity. \;
Host: Richard GreeneSuperconductivity in layered nickelates<
br> Harold Y. Hwang \, Department of Applied Physics\, Stanford
University
Unconventional superconductiv
ity in proximity to various strongly correlated electronic phases ha
s been a recurring theme in materials as diverse as heavy fermion co
mpounds\, cuprates\, pnictides\, and twisted bilayer graphene. Here
we will introduce a new and growing family of layered nickelate supe
rconductors. The initial discovery of superconductivity in infinite-
layer nickelates was motivated by looking for an electronic analog o
f the cuprates. Notable aspects are a doping-dependent superc
onducting dome\, strong magnetic fluctuations\, and a landscape of u
nusual normal state properties from which superconductivity emerges.
The subsequent discovery of superconductivity in bulk La3Ni2O7 unde
r high pressure is quite intriguing\, in that the d-electron configu
ration is a priori quite different. Recently\, we have used epitaxia
l strain in (La\,Pr)3Ni2O7 thin films to stabilize superconductivity
at ambient pressure\, which is promising to extend their exp
erimental study and development.
Host: Johnpierre Pa
glione
When: Tuesday\, January
27\, 2026 - 3:30pm
Where: 1410 Toll Physics Bldg.
REFRESHMENTS SERVED AT 3:00pm
Kagome metals are known for their unique electronic ba nd structure that contains flat bands and Dirac cones with topological char acter. This has elevated interest in kagome metals as an adaptable system to study the interplay of band topology with superconductivity\, itinerant magnetism\, and other charge instabilities that are driven by electronic co rrelations. Here\, we describe inelastic neutron scattering studies of RMn 6Sn6kagome metals where itinerant magnetism within th e Mn kagome layers interacts with the local magnetic moments of interleaved rare-earth (R) triangular layers. We find that competing interlayer magne tic coupling and competing single-ion anisotropies give rise to a variety o f magnetic phases. Transitions between these phases are driven by the uniq ue orbital dynamics of the rare-earth ion. We also provide evidence for it inerant-like flat band and chiral magnetic excitations which may provide a unique window into the correlated electronic states within the kagome layer .
Host: Jeffrey Lynn
The seminar is a
lso on Zoom
Invite Link: https://umd.zoom.us/j/94343757284
1.R.Z. Du et al. Phys. Rev. B 93\, 195402 (2016)
2.S.-Y.Xu et al. Nature Physics 10\, 943-950 (2014)
3.W.Dai et al. Scientific Report < b>7
Title: Quantum interference of hydrodynamic modes despite Planckian \;dissipation in a strang e metal.
Marginal fermi liquid (MFL) p
henomenology was invented30 \;years ago to describe the "strange
metal" phase of the high-Tc \;superconductors. A key featu
re was strong("Planckian") dissipation of \;quasiparticles
\, and the concomitant prediction of linear-T \;resistivit
y. The latter is considered a key experimental hallmark of \;
Title: The low temperature \;thermal Hall conductivity in the Kitaev magnet a-RuCl3
Abstract: The layered h oneycomb Kitaev magnet a-RuCl3 is of strong topical interest. The AF state which appears below 7 K is suppressed when \;B \;(applied al ong the zigzag axis \;a) exceeds 7 T.
The resulting phase is widely regarded as a quantum spin liquid (QSL). The thermal conductivity tensor Kij \;provides an incisive probe of the transport pr operties of the spin excitations.
I will discuss high-resolution meas urements of both Kxx \;and Kxy \;at temperatu res 0.4 K to 10 K with focus on the controversy whether the planar thermal Hall conductivity Kxy \;is half quantized. Our measurements (Ref. 1) support a thermal Hall signal that arises from bosonic edge modes carrying spin excitations in a finite Berry curvature \\Omega. This picture is orthogonal to the Majorana fermion picture advocated by the Kyoto group . I will also describe quantum oscillations observed in Kxx \;inthe QSL state below 4 K. \;
Title: Spinorial hybridization and Majorana physics in tw o-channel Kondo lattices.
< u>
Abstract: The two-channel Kondo lattice hosts a rich array of phases\, perhaps none more interesting than hastatic order\, a channel-symm etry breaking heavy Fermi liquid that has a spinorial order parameter. I w ill discuss our recent insights into the nature of this unusual phase\, inc luding its prevalence in one dimension\; the experimental and computational consequences of the spinorial order\; how it can be realized in intermetal lic materials based on non-Kramers ions like Pr\, U\, and Tm\; and how topo logical defects in the hastatic Kondo insulator can be engineered to host m obile Majorana zero modes or other non-Abelian anyons.
Th e seminar is also on Zoom - Invite Link: https://umd.zoom.us/j/94343757284
Host: Jeffrey Lynn
Refreshments 1:30 pm at 1117 To
ll Physics Bldg.
Ab-initio Simulations of Solid-State Quantum Emitters< /i>
Density functional theory-based simulations are being used in the fields of materials science\, condensed matter physics\, and q uantum chemistry to successfully reveal the underlying physics and chemistr y of a diverse class of materials. I will showcase the power of these simu lations by discussing one of my group’s focus areas – spin active defects i n wide bandgap semiconductors\, which are important for quantum technologie s. Often\, these applications require shallow implantation of defects or th e nanostructuring of the host semiconductors. Our work on defect-based qua ntum emitters in nanostructured silicon carbide shows how different surface effects profoundly influence properties of the near-surface defects. The s econd part of the talk is on high-spin defects in hexagonal boron nitride ( hBN)\, a 2D quantum material. In particular\, I will discuss how the “real- world” conditions – substrates and ambient gases – modulate different prope rties of hBN’s quantum emitters.
Host: Paglione
LAST-MODIFIED:20260414T134442Z LOCATION:1410 John S. Toll Bldg. SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC COLLOQUIUM - Pratibha Dev\, LPS TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20150326T140000 DTEND;TZID=America/New_York:20150326T153000 DTSTAMP:20260524T204340Z UID:q985v6uteua502t37rg0nfh3ok@google.com RECURRENCE-ID;TZID=America/New_York:20150326T140000 CREATED:20150115T203357Z DESCRIPTION:Speaker: James K Glasbrenner\, US Naval Research Lab\, Washing ton\, DC\n\nTitle: Double exchange in the 122 crystal structure: the drive r of ferromagnetic order in (Ba\, K)Mn2As2 and (Ba\, K)(Zn\, Mn)2As2\n\nAbs tract\nThe ThCr2Si2 crystal structure\, also called the 122 structure\, is common in the iron-based superconductivity field. A subset of iron-based su perconductors possess this structure\, with the prototypical example being BaFe2As2. The 122 structure is robust and versatile\, and replacing Fe with another transition metal yields a collection of isostructural materials th at are interesting in their own right. In this seminar I discuss two intrig uing cases\, (Ba\, K)Mn2As2 and (Ba\, K)(Zn\, Mn)2As2\, both of which\, as I will show\, share similar physics in their magnetic interactions.\nThe ma terial BaMn2As2 is an antiferromagnetic Mott insulator with G-type antiferr omagnetic order. Hole-doping the material by replacing a fraction of Ba ato ms with K leads to metallic behavior and a spontaneous\, weak\, in-plane ma gnetization. Using density-functional theory (DFT) calculations\, I show th at the in-plane magnetization can be understood as a small canting of the M n moments that occurs when holes are doped into the system. Further analysi s with a simple tight-binding model and also Andersen force theorem indicat es that canting is due to a competition between an antiferromagnetic supere xchange interaction and a ferromagnetic double exchange interaction.\nThe m aterial (Ba\, K)(Zn\, Mn)2As2 is a recently discovered dilute magnetic semi conductor (DMS). Using DFT calculations\, I show that (i) conventional DFT accurately describes this material\, and (ii) the magnetic interaction emer ges from the competition of the short-range superexchange and a longer-rang e interaction mediated by the itinerant As holes\, coupled to Mn via the Sc hrieffer-Wolff p-d interaction representing an effective Hund's rule coupli ng\, J_H^eff. The key difference between the classical double exchange\, wh ich was at play in (Ba\, K)Mn2As2\, and the actual interaction in this DMS is that the effective J_H^eff\, as opposed to the standard Hund's coupling J_H\, depends on the Mn d-band position with respect to the Fermi level\, and thus allows tuning of the magnetic interactions. The DFT calculations a lso reveal a statistical preference for the formation of nearest-neighbor s inglets\, which explains a puzzling reduction of the magnetization of this material observed in experiment.\n\nHost: Victor Yakovenko LAST-MODIFIED:20150320T180428Z LOCATION:Phys. Rm 1201 SEQUENCE:1 STATUS:CONFIRMED SUMMARY:CNAM Colloquium TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART;TZID=America/New_York:20260129T140000 DTEND;TZID=America/New_York:20260129T143000 DTSTAMP:20260524T204340Z UID:pq93i7keu5vs2dfd0mt32032fp@google.com RECURRENCE-ID;TZID=America/New_York:20260129T140000 CREATED:20250624T150841Z DESCRIPTION:NO TALK THIS WEEK LAST-MODIFIED:20260209T204802Z SEQUENCE:1 STATUS:CONFIRMED SUMMARY:QMC COLLOQUIUM - no talk (Carr Lecture week) TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20170309T190000Z DTEND:20170309T203000Z DTSTAMP:20260524T204340Z UID:0eajme8d9uf8apeb49s990g8f8@google.com CREATED:20170305T204634Z DESCRIPTION:SPEAKER: David Haviland\, KTH Stockholm\n\nTITLE: Quantum Pha se Slips in Josephson Junction Chains\n\nABSTRACT: Quantum fluctuations of the superconducting phase are at the heart of the burgeoning field of circ uit quantum electrodynamics. A fluctuation resulting in a 2 winding is ca lled a phase slip. Coherent quantum phase slips give rise to a Coulomb blo ckade of Cooper pair tunneling\, a remarkable phenomenon with a fascinating duality to the well-known Josephson effects. This talk will discuss both classical and quantum phase slips in one-dimensional Josephson junction arr ays\, focusing on experiments with series chains of SQUIDs. An external ma gnetic flux allows for tuning the chain between the dual regimes of superco nductor and insulator\, resulting in a quantum phase transition.\n\nHOST: Steve Anlage LAST-MODIFIED:20170305T204652Z LOCATION:Room 1201\, John S Toll Physics Bldg. SEQUENCE:0 STATUS:CONFIRMED SUMMARY:CNAM COLLOQUIUM: David Haviland\, KTH Stockholm TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20230921T180000Z DTEND:20230921T193000Z DTSTAMP:20260524T204340Z UID:5fblkk71ssm1767lp8hv3ok6fj@google.com CREATED:20230821T175257Z DESCRIPTION:TBD LAST-MODIFIED:20230821T190741Z LOCATION:Toll Physics Rm 1201 SEQUENCE:0 STATUS:CONFIRMED SUMMARY:QMC COLLOQUIUM (Open) TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT DTSTART:20251211T190000Z DTEND:20251211T203000Z DTSTAMP:20260524T204340Z UID:6dqf4qrmq7ne3e7ane5uqu2pj9@google.com CREATED:20250827T195455Z LAST-MODIFIED:20251203T032436Z LOCATION:1410 John S. Toll Bldg SEQUENCE:0 STATUS:CONFIRMED SUMMARY:NO QMC COLLOQUIUM -Engineering Topological QuantumMatter in Space and Tim e
Topology has emerged as a unifying principle in modern condensed matter physics and materials science\, enabling quantum phases th at are remarkably robust yet exquisitely sensitive to their underlying envi ronment. While traditional approaches to topological materials discovery re ly on chemistry\, the rise of moiré quantum materials suggests a different strategy: engineering topology by tailoring the physical environment.
< p>In this talk I will highlight my group’s recent efforts to control scalab le topological quantum matter using the two most fundamental physical knobs – space and time. We constructed a unique testbed to manipulate and probe materials at femtosecond time scale and atomic-layer spatial scale [1]. In space\, by epitaxially straining topological superconductors FeTexSe1-x to SrTiO3substrates\, we suppress the competi ng antiferromagnetic phase near the FeTelimit and uncover a new tuning mech anism for topological superconductivity: electronic correlations [2]. In ti me\, we show that topological electronic states carry intrinsic layer-depen dent vibrational fingerprints. By “listening” to these frequencies as the s tates couple to coherent phonons\, we develop a quantum stethoscope capable of resolving long-standing puzzles in magnetic topological insulato rs\, including the elusive broken-symmetry energy gap [3\,4].In combined sp ace-time co-engineering\, I will present our latest results\, integrating p hotonic crystal cavities with ultrathin topological insulators to realize c avity-driven Floquet engineering [5]. This platform represents a new class of physical-environment control experiments\, where the ground states of to pological materials are reshaped simultaneously in space and time. Together \, these examples illustrate a paradigm in which topological phenomena can be designed and manipulated by engineering the physical environment\, and p otentially stabilized near ambient conditions – opening pathways toward sca lable quantum materials and devices.[1] C. Yan et al. Rev. Sci. I nstrum. 92\, 113907 (2021)
[2] H. Lin et al. Nat ureComm. 17\, 1188 (2026)
[3] W. Lee et al. Nature Phys . 19\, 950 (2023)
[4] K. D.Nguyen et al. Science Advances 10\, eadn5696 (2024)
[5] Y. Bai et al. in prep aration
Title: 1D topological systems for n ext-generation electronics \;
Abstract: Topological nanowires\, topological materials confined in one dimension (1D)\, hold gre at promise for robust and scalable quantum computing and low-dissipation in terconnect applications\, which will transform current computing technologi es. To do so\, research in topological nanowires must continue to improve t heir synthesis and properties.
In this talk\, I will discuss my group ’s efforts to develop a high throughput and precision synthesis method to f abricate 1Dtopological systems. I will also highlight our recent studies on topological metal MoP nanowires and discuss their potential applications. Finally\, I will present phase transformations present in these topological systems and how to study them using cryo STEM.
Interactions between electrons in solids are resp onsible for a wide variety of physical phenomena such as magnetism\, superc onductivity Mott insulators and more. Understanding interactions between el ectrons\, and manipulating them to stabilize desired electronic phases have been the research focus of the strongly correlated electrons community in the past few decades. Ultrafast optics is a unique experimental platform wh ere strong ultrashort pulses of light can be used both to probe a multitude of electronic phenomena\, and to excite and manipulate the properties of t he electronic system\, driving it away from its equilibrium state. In this talk I will show how ultrafast optical techniques can be used to probe shor t range spin correlations and modify magnetic interactions in a 2D layered ferromagnet. CrSiTe3 is composed of weakly bonded sheets of ferromagnetical ly interacting Heisenberg spins that\, in isolation\, would be impeded from long range order by the Mermin-Wagner theorem. I will show that CrSiTe3 ev ades this law via a two-step crossover from two- to three-dimensional magne tic short range order above its Curie temperature (Tc = 31 K)\, manifested through two previously undetected totally symmetric distortions at T2D ~ 11 0 K and T3D ~ 60 K serving as a direct probe for measuring intarlayer and i nterlayer short range spin correlations. Having understood the interplay be tween short range correlations and the magneto-elastic distortions I will s how how optically induced charge transfer could be used to enhance the magn etic super-exchange interaction and how this manipulation can be detected b y phase resolved spectroscopy of coherent phonons.
Host: TakeuchiRef: S. Kim\,Y.Lv\, ….\, F. Mahmood. “Observation of a massive phason in a charge density waveinsulator ”. Nature Materials 22\, 429-433 (2023).
Host: Paglione
The seminar is also on Zoom\, Invite Link: https://umd.zoom.us/j/94343757284
Refres
hments 1:30pm 1117 Toll Physics Bldg.
Department of Electrical and ComputerEngineering\, University of Maryland\ , College Park
2D Magnets and 2D Magnetism
Magnetism\,one of the most fundamental physical properties\, has revo lutionized significanttechnologies such as data storage and biomedical imag ing\, and continues tobring forth new phenomena in emerging materials of re duced dimensionalities.The recently discovered magnetic 2D van der Waals ma terials provide idealplatforms to enable the atomic-thin\, flexible\, light weight magneto-optical andmagnetoelectric devices. Though many have hoped t hat the ultra-thinness of 2Dmagnets should allow an efficient control of ma gnetism\, the state-of-the-art hasnot achieved notable breakthroughs to thi s end. In this talk\, I will speak onour experimental discovery of the firs t 2D ferromagnet\, and discuss our recentprogress in the efficient electric al and optical control of 2D magnetism.
Link: \;https://umd.zoom.us/j/91251230757?pwd=<
/u>MkhFREJrUXNTekVZTTRGQ244M1VBZz09
Meet
ing ID: \;912 5123 0757
Password: \; \; 558484
Title: How material \;and de sign of superconducting qubits affect quasiparticles
\;Cihan Kurter\, IBM Quantum\, T. J. Watson Research Center\, Yorktown Heights NY\ , United States.
Abstract: Elementary excitations of the super conducting condensate known as quasiparticles are major sources of dissipat ion in superconducting qubits. When a quasiparticle tunnels across the Jose phson junction (JJ) of a qubit circuit\, there is a possibility of exchangi ng energy with the qubit\, leading to a total decoherence. In this talk\, I will mainly focus on the impact of intrinsic habitat of two-dimensional\, fixed frequency transmon qubits such as shunting capacitor material or desi gn on the quasiparticle dynamics. I will also present our recent results on temperature dependence of quasiparticle tunneling rate to discuss how quas iparticles respond to high transmission sites/defects within the oxide barr iers of the JJs. Our results demonstrate a unique in situ characterization tool to assess the uniformity of tunnel barriers in qubit junctions and she d light on how quasiparticles can interact with various elements of the qub it circuit.
Host: Palmer \;
The exciton\, a bound state of an electron and a hole\, is a fundament al quasiparticle induced by coherent light-matter interactions in semicondu ctors. Such Coulomb-bound states have gained significant interest due to th eir critical roles in both fundamental science and technological applicatio ns. Concurrently\, recent advancements in the study of topological phases o f matter have shed light on new routes in materials science\, leading to th e discovery of unique phases and properties\, such as spin-polarized surfac e states in topological insulators. One of the ultimate frontiers in these fields is to create excitonic states coupled with topological quasiparticle s\, to leverage both topological effects and excitonic correlations simulta neously. However\, numerous questions remain\, particularly regarding wheth er excitonic states can be induced in the presence of topological invariant s\, how these properties manifest in the material’s electronic structures\, and what properties of the topological states persist. In this talk\, I wi ll present our recent work[1]\, which reports the direct observation of exc itonic states in a topological insulator measured by ultrafast angle-resolv ed photoemission spectroscopy. This work reveals the conditions under which excitonic states can be driven in topological insulators\, as well as the unique excitonic signatures that emerge in topological states and the topol ogical signatures induced in the excitonic states. Future directions for ex ploring and manipulating the excitonic topological states will also be disc ussed. This research opens up a new platform for probing exciton-mediated s tates in topological materials and investigating their potential applicatio ns.
[1] R. Mori et al.\, Nature 614\,249–255 (2023)
Refreshments - 3:30 pm at 1117 Toll Physics Bldg.<
/b>
Title:
Materials discovery of next-gene ration quantum materials\, the AV3Sb5 \;(A: K\, R b\, Cs) kagome superconductors
Abstract:
New materials d iscovery has been a fundamental part of the synthetic chemistry\, condensed matter physics\, and materials fields. The targeted synthesis of new terna ry and quaternary compounds has immense potential for introducing new chemi cal complexity and diversity into the known model systems. Our discovery of the AV3Sb5 \;(A: K\, Rb\, Cs) kagome superconduc tors is a prime example of how rational exploration of phase space can lead to untold opportunity. The AV3Sb5 \;materials ar e quasi-2D (structurally and electronically)\, exfoliatable\, air-stable\, metals with a structurally perfect kagome network of vanadium. The entire f amily exhibits competition between charge density wave (CDW) order below (8 0-100K)\, and a superconducting (Tc = 0.9-2.5K) ground state. Our work indi cates that the systems are topologically nontrivial\, and surface states sh ould be close to the natural Fermi level. A complex interplay between the e lectronic properties and the CDW is observed\, with the possibility of a ch iral CDW as the source of anomalous Hall effect in the entire family. In th is seminar I will describe the rapidly growing body of knowledge surroundin g the AV3Sb5 \;system\, including potential topol ogical surface states\, unconventional superconductivity\, and interplay of charge density wave order and superconductivity.
Title: \;Probi ng quantum materials with the lens of machine learning \;
Abst
ract: Despite the significant progress in experimental techniques\, und
erstanding the microscopic interaction mechanisms in a quantum material rem
ains a grand challenge. With monotonically increased experimental data\, ma
chine learning (ML) brings new hope and can serve as a new probe to study t
he complex interplay between the charge\, orbital\, spin\, and lattice degr
ees of freedom. In this colloquium\, I will introduce how ML can be used to
reveal the hidden information in experimental data and elucidate the quant
um materials. I will provide a few examples from our research\, that 1) how
ML can help identify the proximity effect\, an effect that can lead to dis
sipationless spintronics or topological quantum computing\, 2)how ML can be
used to analyze spectra to reach topological materials classification\, an
d 3) how ML can result in interfacial defects identification with unprecede
nted knowledge\, and magnetic structure identification through architecture
design. We highlight the importance of the representations and envision a
variety of problems that can benefit from machine learning.
\;[1] https://onlinelibrary.wiley.com/doi/10.1002/advs.202004214 \;
[2] https://aip. scitation.org/doi/10.1063/5.0049111
[3] https://arxiv.org/abs/2003.00994
[4] https://arxiv.org/abs/2109.08005
VIRTUAL Seminar on Zoom
Meeting \;Link: \; \;
https://umd.zoom.us/j/913010758
48
[1] C. Chen etal. Phys. Rev. B 95\, 094111 (2017). Exploring new
phases of matter and understanding their physics are at the forefront of co
ndensed matter physics. The discovery of moiré materials has revolutionized
this pursuit\, providing a simpler and more controllable approach to inves
tigating complex phenomena. Beyond geometry and symmetry\, electron band to
pology and electron-electron correlations are pivotal in understanding and
harnessing the unique properties of quantum materials. In my talk\, I will
demonstrate how we use the power of 2D quantum materials to simulate topolo
gical and many-body Hamiltonians by two examples. First\, I will explain ou
r discovery of the Haldane Chern insulator by splitting a quantum spin Hall
insulator into two halves: one topologically trivial and the other nontriv
ial. Second\, I will describe the realization of a synthetic Kondo lattice
in AB-stacked MoTe2/WSe2 moiré bilayers\, where the MoTe2 layer is tuned to
a Mott insulating state\, supporting a triangular moiré lattice of local m
oments and the WSe2 layer is doped with itinerant conduction carriers. Fina
lly\, I will conclude by highlighting many exciting new possibilities in 2D
quantum materials. By combining complementary techniques\, we not only open
new avenues in the study of quantum materials but also lay the groundwork
for future technological innovations. Re
freshments - 3:30 pm at 1117 Toll Physics Bldg. Magnetic Correlations in (FexCo1-x)NGeTe2 van der Waals Crystals In recent years\, two-dimensional (2D) materials have been
at the forefront of condensed matter research. The discovery of long-range
magnetic order in 2D materials* has catapulted the search for new van der W
aals (vdWs) materials with stable magnetic ordering above room temperature.
An emergent class of such magnets is the compounds (Fe1-xD
x)NGeTe2(N = 3\, 4\, and 5 and D
= Ni or Co). In this talk\, I will discuss the state of magnetic ordering o
ver a wide field–temperature phase space in single crystals of the high-
Tc ferromagnet (Fe1-xDx)NGeTe2 studied using magnetization\, ferromagnetic resonance
(FMR)\, and electrical transport measurements. For the x = 0 compounds\, o
ur findings demonstrate an amagnetic phase transition from a collinear to a
complex non-collinear magnetic order near the temperature T* ≈ 160
K\, below which the magnetic susceptibility is reduced\, the FMR linewidth
broadened\, and the anomalous Hall resistivity suppressed. I will also disc
uss how the insertion of Co and Ni at the Fe sites affects these results an
d leads to new magnetic phases. * 1)Jae – Ung Lee et al (Nano Lett. 1
6\, 7433 (2016)) 2) C. Gong et al (Nature 546\, 265 (1017) 3)
Bevin Huang et al (Nature 546\, 270 (2017) This research has
been conducted jointly with postdoctoral associate Rabindra Basnet and fun
ded by the DOD Center of Excellence on 2D materials research under grant No
. W911NF2120213. Title: Topology\, Superconductivity and Unconventiona
l Quantum Criticality in Monolayer WTe2 Abstract: Quantum critical po
ints associated with quantum phase transitions are highly intriguing states
of matter\; yet they are difficult to study. An example is the superconduc
tor to insulator or metal transition in two dimensions (2D)\, a topic that
has a long history in condensed matter research\, but many problems remain
unsolved. In this talk\, I will discuss our recent experimental finding of
a quantum critical point in monolayer tungsten ditelluride (WTe2)\, a uniqu
e 2D crystal in which topology\, strong correlations and superconductivity
all occur in a single material. We directly measure superconducting quantum
fluctuations\, whose behaviors are so anomalous that an unusual explanatio
n beyond the conventional Landau-Ginzburg-Wilson paradigm is required. Meeting ID: 912 5123 0757 Quantum circuit elements using nitride superconductors Future advances in qubit performance are likely t
o be unlocked through materialimprovements for linear and nonlinear superco
nducting circuit elements. Through a structure-property-performance framewo
rk\, nitride superconducting thin filmswill be explored for use as resonato
r and Josephson junction components. Specifically\, Plasma Assisted Molecul
ar Beam Epitaxy (PAMBE) is used to synthesize nitride binary and ternary co
mpounds such as TiN\, NbN\, ZrN\, NbTiN\,&\; ZrTiN on sapphire wafers. A
lloyed thin films that have an engineered lattice constant are designed and
synthesized to match the in-plane atomic spacing of nitride dielectric mat
erials such as AlN &\; ScN. The films are grown at temperatures below 10
00 oC\, exhibit a superconducting critical temperature over 15 K
\, a root-mean-square surface roughness less than 1 Å\, internal quality fa
ctors at low powers above 2M\, non-saturating loss-behavior at high powers\
, and low kinetic inductance. Insight fromprototype trilayer materials and
epitaxial Josephson junctions identify additional material challenges and p
otential for qubit devices that operate at higher temperatures Host: Paglione Abstract:
Error-corrected quantum computing demands seamless integration of 10s of th
ousands of qubits. While superconducting qubits take the leading role in ne
ar-term quantum computing\, their scaling is limited by the errors and loss
es in individual qubits as well as the size of the comprising microwave com
ponents\, and the cryostat that houses them. This beckons extensive materia
ls research to engineer platforms ideal for fault-tolerant and scalable qua
ntum hardware. Here\, I discuss hybrid superconductor-semiconductor (super-
semi) materials systems as promising platforms for scalable quantum circuit
s by enabling dissipationless tuning of superconducting qubits and couplers
. I will provide an overview of the advances and limitations of the state-o
f-the-art voltage-tunable superconducting quantum devices demonstrated on t
he hybrid Al-InAs systems. I will then discuss a few strategies to break th
rough the existing barriers for voltage-tunable devices by integrating the
more robust group IV semiconductors into hybrid super-semi systems. Through
this approach\, I hope to emphasize the significant role materials physics
plays in the development of emerging quantum hardware. Refreshments at 1:30 pm - 1117 John S. Toll Bldg Link: \;https://umd.zoom.us/j/912512
30757?pwd=MkhFREJrUXNTekVZTTRGQ244M1VBZz09 Meeting ID: \;912 5123 0757 Recent advances in optical nanoscopy with quantum mate
rials In this talk\, I will introduce two emer
ging optical nanoscopy techniques and the new science they enable. These te
chniques\, namely magneto-scanning near-field optical microscopy (m-SNOM) a
nd Bolometric Superconducting Optical Nanoscopy (BOSON)\, can dramatically
expand our ability to probe quantum materials at the nanoscale. Using m-SNO
M\, we demonstrate Landau-level nanoscopy that directly visualizes Landau q
uantization and magneto-polariton formation. A waveguide quantum electrodyn
amics (QED)framework reveals spatially resolved hybridization between magne
tic excitations and phonon polaritons\, yielding universal scaling behavior
s and design principles for cavity metastructures with tunable light–matter
coupling. With BOSON\, we integrate superconducting transition-edge sensor
s with near-field optics to achieve ultra-sensitive detection of nano-light
at nanowatt power levels. This platform enables nanoscale imaging of Coope
r pair dynamics and confined bosonic modes in low-dimensional systems\, off
ering a new pathway toward quantum-limited spectroscopy and single-polarito
n detection. I will conclude by discussing future directions\, including th
e integration of these techniques for exploring THz quantum optics\, polari
tonic circuitry\, and strongly correlated quantum phases in complex materia
ls. Meeting ID: \;912 5123 0
757 Jochen Mannhart Max Planck Institute for Sol
id State Research Stuttgart\, Germany Advanced Epitaxial Growth of Quantum Materials Usi
ng Thermal Laser Epitaxy We have developed a
thin-film deposition technique suited for the growth of an extremely wide
range of quantum materials with atomic precision (e.g.\, [1–4]). Th
is technique\, called thermal laser epitaxy\, utilizes laser-induced therma
l evaporation of ultrapure sources\, enabled by unlimited evaporation tempe
ratures. Furthermore\, a CO2-laser-based substrate heating system provides
virtually restricted growth temperatures in almost any background gas. As a
result\, thermal laser epitaxy exceeds the capabilities of molecular beam
epitaxy and pulsed laser deposition in key aspects\, for example\, by enabl
ing adsorption-controlled growth of quantum materials with unprecedented pu
rity. In this seminar\, I will discuss the state<
span> of the art of the
growth of quantum materials using thermal laser epitaxy and the opportunit
ies this advanced technique offers for the epitaxial growth of complex film
s and heterostructures. [1] W. Braun and J. Man
nhart\, AIP Adv. 9\,085310 (2019) Refreshments at 3:30 pm - 1117 Toll Physics Bldg. Title: Magnetically Confined Quasiparticles in Quantum Ma
tter Abstract: Quasiparticles
\, the collective excitations that emerge from the interactions of many
particles\, have captivated physicists for decades. Unlike the dozens of f
undamental particles that are the building blocks of the known universe\, q
uasiparticles are emergent and constantly advancing our understanding of ma
terials. Novel quantum phenomena often emerge when new approaches to confin
e the underlying quasiparticles are developed. In this talk\, I will highli
ght our recent work on low-dimensional quasiparticles realized by magnetic
confinement. In the first example\, I will explain how the complex momentum
-space structures of Dirac nodal-lines can host exotic quasiparticles that
are massless in one direction and massive in the perpendicular direction. T
hese so-called semi-Dirac fermionsignited intense theoretical interest sinc
e their prediction more than 16 years ago\, but remain undetected. Using ma
gneto-optical spectroscopy\, we demonstrate the defining feature of semi-Di
rac fermions –scaling of Landau levels– in a prototypical nodal-line metal
ZrSiS. For the second example\, I will report a previously unidentified typ
e of optical excitation – a magnetic surface exciton – enabled by the antif
erromagnetic spin correlations that confine excitons to the surface. By que
nching interlayer interactions\, the antiferromagnetic order of CrSBr stric
tly confines the bound electron-hole pairs within the same layer\, regardle
ss of the total number of layers and without the need of external magnetic
fields. Link: \;https://umd.zoom.us/j/91 Meeting ID: \;912 5123 0757 DEMO: There will be
an exciting live demo of an electrical tree formation! Jochen Mannhart Max Planck Institute for Sol
id State Research Stuttgart\, Germany Action at the Edge: Interfaces in Sup
erconductors and Outlaw QuantumSystems I
n this colloquium\, we will embark on a fascinating journey to the frontier
s of condensed matter physics\, exploring the intriguing world of supercond
uctors and the territory of ‘outlaw’ quantum systems. Superconductors\, kn
own for their zero electrical resistance\, have long been a subject of inte
nse study. Critically\, when interfaces are embedded into superconductors\,
they generate a rich variety of emergent properties\, which lay the founda
tion for intriguing questions of fundamental physics as well as for applica
tions such as the exploration of mineral resources or nuclear fusion. Does
nature prohibit practical zero-resistance cables that operate at room tempe
rature and run by a mechanism other than superconductivity? Following up on
this apparently absurd notion\, I will present quantum thermodynamic devic
es that utilize the strange phenomena occurring at the interface between th
e quantum and the classical worlds. These devices violate well-accepted law
s and rules and enable revolutionary materials and technologies. This collo
quium aims not only to inform but also to inspire by posing unanswered ques
tions and suggesting potential paths for future research. Refreshm
ents will be served at 3:30 p.m. Fractional Quantum Anomalous Hall Effects in Multilayer G
raphene Interactions between electrons in solids
often lead to exotic states of matter that are beyond single-particle pict
ures. One paradigmatic example is the fractional quantum Hall effect\, wher
e the Hall resistance in a two-dimensional electron gas is quantized at fra
ctional multiples of h/e^2 in high magnetic fields. Some of these exotic fr
actional excitations were thought to be the key for performing topological
quantum computation\, in which the qubits are protected by their topologica
l properties from the disturbance of the environment. It has been a long-st
anding question whether fractionally quantized Hall resistance can exist wi
thout a magnetic field until clues appeared very recently in two-dimensiona
l materials systems. In this talk\, I will present the experimental observa
tion of the fractional quantum anomalous Hall effect\, a lattice analogue o
f the renowned fractional quantum Hall effect at zero magnetic field\, in a
rhombohedral pentalayer graphene/hBN moire superlattice. Then\, I will dem
onstrate rhombohedral pentalayer graphene/hBN as a new platform that holds
significant potential for exploring fractional excitations and statistics\,
especially considering the uncharted big phase space spanned by the layer
number\, the twist angle between graphene and hBN\, as well as the tuning o
f the gate electric field. It further paves the way to engineer the more ex
otic parafermions (obeying non-Abelianstatistics that can be used for topol
ogical quantum computation) by combining with superconductivity. Refreshments - 1:30 pm at 1117 Toll Physics Bldg. Title: Listening to the sound of superfluid Abstract: The exploration of unconventional superconductivity h
as entered a new frontier with the emergence of exotic phases in quantum ma
terials—from moiré superlattices to topological semimetals. Probing the sup
erfluid properties and pairing symmetry in these systems is essential to un
derstanding their unconventional behavior\, yet traditional techniques ofte
n falter when applied to atomically thin materials or those with extremely
low critical temperatures. Here\, we present a novel approach that “listens
to the sound of superfluid” by probing the kinetic inductance of supercond
uctors through microwave resonant cavities. Variations in superfluid stiffn
ess perturb the cavity resonance frequency\, enabling precise measurements
of the London penetration depth with parts-per-million sensitivity. This te
chnique provides unprecedented access to the superfluid response in fragile
and low-temperature superconductors. Applied to magic-angle-twisted trilay
er graphene and the Weyl semimetal MoTe₂\, our measurements uncover compell
ing signatures of nodal superconductivity. In twisted trilayer graphene\, w
e observe a linear temperature dependence of the superfluid stiffness and a
zero-temperature stiffness that scales linearly with the critical temperat
ure—echoing Uemura’s relation in cuprates. In MoTe₂\, the penetration depth
exhibits a T2 dependence down to millikelvin temperatures. Most
strikingly\, both systems display the anomalous nonlinearMeissner effect\,
where the superfluid response becomes current-dependent—a hallmark of noda
l quasiparticles. These results offer evidence for unconventional pairing i
n both moiré and topological superconductors\, demonstrating how “listening
” to the subtle resonances of quantum fluids can illuminate the hidden symm
etries of correlated electron matter. Ref.: A. Banerjee\, et.
al.\, Nature 638\, 93 (2025). The intermetallic c
ompound URu2Si2 is among the best-known cases of
correlated electron physics\, highlighting the difficulty that we still hav
e accurately describing interactions involving electrons originating in f-o
rbitals. \; The most glaring manifestation of our lack of
understanding is the Hidden Order phase\,characterized by a clear phase tra
nsition\, but an experimentally undetermined order parameter that remains e
lusive despite 30 years of looking. In this
talk\, I will describe how hybridization between uranium f-electrons and i
tinerant electrons leads to clear temperature-dependent correlations and a
very unusual ground state. I will discuss neutron scattering measurements o
n Fe-substituted samples\, in which Hidden Order transitions to antiferroma
gnetism\, and what we can say about how the electronic structure in both ph
ases. I will also discuss resonant inelastic x-ray scattering
measurements aimed at identifying the degrees of freedom available to the u
ranium f-electrons and how this relates to the collective low-temperature g
round state. Opportunities and Challenges of Complex Oxide Membrane
s The growing demand for integr
ating functional oxides onto dissimilar substrates has driven extensive res
earch into detaching functional thin films from their original substrates t
o form membranes\, enabling vertical or back-end-of-the-line (BEOL)integrat
ion. These functional oxide membranes\, while exhibiting intriguing propert
ies under extreme strain or free from clamping effects\, present challenges
in synthesizing high-quality films. In this presentation\, I will discuss
the challenges involved in synthesizing three-dimensional (3D) perovskite n
anomembranes and the innovative approaches our group has developed to overc
ome these obstacles. Utilizing hybrid molecular beam epitaxy (MBE) with a m
etal-organic precursor\, titanium isopropoxide\, we successfully grew epita
xial SrTiO3 (STO) and BaTiO3 (BTO)films directly on graphene layers that were transferred onto bulk ST
Osubstrates. These films were then exfoliated and transferred onto various
other substrates. Additionally\, I will showcase a sacrificial layer method
that enables the creation of oxide membranes with a room-temperature diele
ctric constant of approximately 300. The talk will conclude with an explora
tion of the potential applications of 3D nanomembranes in materials physics
and device engineering.
[2]L. Guarneri et al.\, Adv. Mater. 33\, 2102356
Host: Richard Greene
Location: Toll Physics Rm 1201
Seminar also on Zoom
Invite Link: https://umd.zoom.us/j/94343757284
Refreshme
nts 1:30pm 1117 Toll Physics Bldg.
LAST-MODIFIED:20230821T194220Z
LOCATION:Toll Physics Rm 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: Ricardo Lobo\, PSL University\, France
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20151203T190000Z
DTEND:20151203T203000Z
DTSTAMP:20260524T204340Z
UID:ikcaubh1rleokj02cqabf1j4t0@google.com
CREATED:20150831T185853Z
DESCRIPTION:SPEAKER: Kevin Osborn\, UMD\n\nTITLE: The Tunneling Atom Laser
: Manipulating lossy two-level defects to produce coherent microwave gain i
n a resonator\n\nABSTRACT: Superconducting qubits have coherence limitatio
ns set by two-level system (TLS) defects which absorb microwave energy. The
se TLSs are known to arise in dielectric films such as native oxides\, at m
aterial interfaces\, etc. As a result\, TLSs contribute to damping in qubit
s and related parametric amplifiers\, where a Josephson junction is used fo
r the nonlinearity. Here I will show a new method to adiabatically invert (
excite) these same TLSs using a resonator which has no other significant no
nlinearity. Pump fields are applied at detuned frequencies from the resonat
or\, and with an additional sweeping dc field\, the TLS population is gener
ally inverted. When TLSs are inverted we find that they produce gain nonlin
earity rather than a damping contribution. This occurs despite TLS randomne
ss in multiple standard model parameters. We show that the threshold for la
sing can be explained in terms of a cavity quantum electrodynamics model. F
urthermore\, with this control\, the resonator is found to pass from the re
gime of ordinary defect loss\, through a state of negligible material dissi
pation (and infinite quality factor)\, and finally to a regime of coherent
microwave gain.
LAST-MODIFIED:20151127T230323Z
LOCATION:Room 1201 John S Toll Physics Bldg.
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Kevin Osborn\, UMD
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20200423T180000Z
DTEND:20200423T190000Z
DTSTAMP:20260524T204340Z
UID:712h3ju0b17vbfqq5mmfpc60q0@google.com
CREATED:20191212T191129Z
LAST-MODIFIED:20200108T211225Z
LOCATION:Room 1201 of the John S. Toll Building
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM:
Host: Rick Greene
Refr
eshments at 1:30 pm - 1117 John S. Toll Bldg
LAST-MODIFIED:20251001T213448Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM - Ramesh Budhani\, Morgan State
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20200917T140000
DTEND;TZID=America/New_York:20200917T153000
RRULE:FREQ=WEEKLY;WKST=SU;UNTIL=20201128T045959Z;BYDAY=TH
EXDATE;TZID=America/New_York:20200917T140000
EXDATE;TZID=America/New_York:20201001T140000
EXDATE;TZID=America/New_York:20201022T140000
EXDATE;TZID=America/New_York:20201029T140000
EXDATE;TZID=America/New_York:20201105T140000
EXDATE;TZID=America/New_York:20201112T140000
EXDATE;TZID=America/New_York:20201119T140000
EXDATE;TZID=America/New_York:20201126T140000
DTSTAMP:20260524T204340Z
UID:607qfp6ecj8s8f6f3eapn8jv2d@google.com
CREATED:20200901T143220Z
DESCRIPTION:Speaker: TBA\nAbstract: TBA\nHost: TBA\n\nFor the zoom link ple
ase email Kristin Stenson at QMC@umd.edu
LAST-MODIFIED:20201016T183115Z
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM:
Location: Toll Physics Rm 1201
Seminar also on Zoom
Meeting Link: https://umd.zoom.us/j/91301075848
LAST-MODIFIED:20230427T170505Z
LOCATION:Toll Physics Rm 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: Sanfeng Wu\, Princeton University
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20181115T140000
DTEND;TZID=America/New_York:20181115T153000
DTSTAMP:20260524T204340Z
UID:3faclu8nhnvc7ugv0ad0tvoimk@google.com
RECURRENCE-ID;TZID=America/New_York:20181115T140000
CLASS:PUBLIC
CREATED:20180117T225437Z
DESCRIPTION:Title: Strain-tuned topological phase transition in ZrTe5\n\nSp
eaker: Jiun-Haw Chu\, University of Washington\n\nAbstract: \nBand insulato
rs with time reversal symmetry can be classified into normal insulators (NI
)\, weak topological insulators (WTI) and strong topological insulators (ST
I) based on their Z2 topological indices. Changing Z2 indices requires clos
ing and reopening the bandgap\, and topologically distinct insulating phase
s are separated by a gapless Dirac or Weyl semimetal phase. The van der Waa
l layered material ZrTe5 is a prototypical example that the emergence of ma
ssive 3D Dirac fermions is due to its proximity to the STI-WTI phase bounda
ry. In this talk\, I will demonstrate that a STI-WTI topological phase tran
sition can be induced by applying uniaxial stress to ZrTe5\, and make the c
ase that the in-situ tunable strain is a powerful to study and control topo
logical materials. In addition\, due to the low carrier density in this mat
erial\, the lowest Landau level can be reached within a few tesla of magnet
ic field. I will describe the unusual angle dependent magnetotransport beha
vior in the quantum limit magnetic fields.\n\n\nHost: Paglione
LAST-MODIFIED:20181105T224155Z
LOCATION:Room 1201 John S Toll Bldg
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:CNAM COLLOQUIUM: Jiun-Haw Chu\, University of Washington
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250911T140000
DTEND;TZID=America/New_York:20250911T143000
RRULE:FREQ=WEEKLY;WKST=SU;UNTIL=20251204T045959Z;BYDAY=TH
EXDATE;TZID=America/New_York:20250911T140000
EXDATE;TZID=America/New_York:20250918T140000
EXDATE;TZID=America/New_York:20250925T140000
EXDATE;TZID=America/New_York:20251002T140000
EXDATE;TZID=America/New_York:20251009T140000
EXDATE;TZID=America/New_York:20251016T140000
EXDATE;TZID=America/New_York:20251023T140000
EXDATE;TZID=America/New_York:20251030T140000
EXDATE;TZID=America/New_York:20251113T140000
EXDATE;TZID=America/New_York:20251127T140000
EXDATE;TZID=America/New_York:20251120T140000
DTSTAMP:20260524T204340Z
UID:6o92asm2j4le18g6ktiqf8qbij@google.com
CREATED:20250624T150841Z
DESCRIPTION:HOST:
LAST-MODIFIED:20251103T150203Z
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM - (OPEN/TBD)
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150319T140000
DTEND;TZID=America/New_York:20150319T153000
DTSTAMP:20260524T204340Z
UID:q985v6uteua502t37rg0nfh3ok@google.com
RECURRENCE-ID;TZID=America/New_York:20150319T140000
CREATED:20150115T203357Z
DESCRIPTION:SPEAKER: Prof. Joel Moore\, UC - Berkeley\n\nTITLE: Dynamical
consequences of non-Abelian gauge fields and non-Abelian particles in solid
s\n\nABSTRACT: An electron moving through a crystal ceases to be a feature
less point particle and acquires structure within the unit cell\, with far-
reaching consequences. Although the forces acting on the electron are elec
tromagnetic and hence described by a simple (Abelian) gauge theory\, the in
ternal structure gives Berry gauge fields that are non-Abelian in the same
sense as the fields of quantum chromodynamics (QCD). The Berry gauge field
s give the most compact description of the 3D topological insulator phase a
nd lead to a general theory of orbital magnetoelectricity. Recent work sug
gests that long-standing experiments on natural optical activity (NAO) also
probe these Berry gauge fields. Taking the topological insulator phase an
d adding superconducting correlations is one of several experimentally prom
ising routes to create particles with non-Abelian statistics\, such as an e
mergent Majorana fermion excitation. We explain non-Abelian statistics bri
efly and discuss recent work on how quantum quench dynamics can show univer
sal power laws characterizing various non-Abelian particles. These power l
aws can be observed in optical absorption\, similar in spirit to the classi
c orthogonality catastrophe in X-ray absorption.\n\n
LAST-MODIFIED:20150312T195341Z
LOCATION:Phys. Rm 1201
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Joel Moore\, Berkeley
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230223T140000
DTEND;TZID=America/New_York:20230223T153000
DTSTAMP:20260524T204340Z
UID:5sqgc92ns31ji7fi7f56lcl20q@google.com
RECURRENCE-ID;TZID=America/New_York:20230223T140000
CREATED:20220829T135334Z
DESCRIPTION: Title: Towards Ultra-Low-Power and Scalable 2D Topological Spi
ntronics Using
Quantum Materials
The current electronics industry
is facing challenges both from the fundamental physics limit of silicon on
the small scale\, and the new demand for big-data applications on the larg
e scale. Spintronics\, utilizing spin degree of freedom\, is a promising fo
r future beyond-CMOS devices and systems\, thanks to their low power consum
ption\, nonvolatility\, and easy 3D integration. The emerging 2D magnets ca
n preserve single-phase magnetism even in monolayer (~0.8 nm) limits\, and
thus they are promising to further scale down devices. They have a sharp in
terface and atomically thin nature\, promising for designer quantum devices
and more functionalities (e.g. stacking order\, twist angle\, thickness\,
and voltage control). In this talk\, I will discuss 2D spintronics with qua
ntum devices on skyrmions and antiferromagnets\, and their potential applic
ations. I will begin by presenting my observations of real-space topologica
l spin textures - magnetic skyrmions\, in 2D devices. This work represents
the first report of skyrmion lattice imaging in 2D layered magnets. Buildin
g on this\, I will present my findings on the vertical imprinting of skyrmi
ons onto neighboring layers in a 2D ferromagnet/2D ferromagnet system\, dem
onstrating new functionality for skyrmion-based spintronics. I will then di
scuss the exchange coupling and voltage controlled 2D antiferromagnetism\,
a step towards energy-efficient and fast spintronics. In addition\, future
work on quantum materials is motivated that would focus on energy-efficient
control in magnetism\, for neuromorphic and quantum computing.
Location: Toll Physics Rm 1201
Seminar also on Zoom
Meeting Lin
k: https://umd.zoom.us/j/91301
075848
Refreshments 1:30pm 1117 Toll Physics
Bldg.
LAST-MODIFIED:20230214T165540Z
LOCATION:Toll Physics Rm 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: YingYing Wu\, MIT
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150507T140000
DTEND;TZID=America/New_York:20150507T153000
DTSTAMP:20260524T204340Z
UID:q985v6uteua502t37rg0nfh3ok@google.com
RECURRENCE-ID;TZID=America/New_York:20150507T140000
CREATED:20150115T203357Z
DESCRIPTION:SPEAKER: Prof. Philip Kim\, Harvard\n\nTITLE: Materials in 2-d
imension and beyond: 10 years after graphene\n\nABSTRACT: The recent adven
t of atomically thin 2-dimensional materials such as graphene\, hexa boroni
tride\, layered transition metal chalcogenide and many strongly correlated
materials\, has provide a new opportunity of studying novel quantum phenome
na in low dimensional systems. In particular\, graphene has been provided u
s opportunities to explore exotic transport effect in low-energy condensed
matter systems. Moreover\, combination of different layered constituents ma
y produce heterogeneous and functional materials. In this presentation\, we
will discuss novel electron transport phenomena across the heterointerface
s in atomically controlled van der Waals quantum heterostructures.\n\nHOST:
James Williams
LAST-MODIFIED:20150423T165355Z
LOCATION:Phys. Rm 1201
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Philip Kim\, Harvard
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210211T140000
DTEND;TZID=America/New_York:20210211T153000
RRULE:FREQ=WEEKLY;WKST=SU;UNTIL=20201202T045959Z;BYDAY=TH
DTSTAMP:20260524T204340Z
UID:4snvub7j554m88s6sii5bj2u93@google.com
CREATED:20210204T152334Z
DESCRIPTION:Speaker: tba
Title: tba
Abstract: tba
H
ost: tba
Link: https://umd.zoom.us/j/91251230757?pwd=MkhFREJrUXNTekVZTTRGQ244M1VBZz
09
Joe Checkelsky's Meeting Schedule \; \;
Title: Synthesizin
g “Toy Model” Quantum Materials" \; \;
Abstract:
Connecting t
heoretical models for exotic quantum states to real materials is a key goal
in quantum material synthesis. Among such theoretical models\, a “toy mode
l” is one made deliberately simplistic in order to demonstrate new physical
concepts and their underlying mechanisms. We describe here our recent pro
gress in experimentally realizing “toy model” quantum materials which\, in
analogy to their theoretical counterparts\, are designed to capture simple
model systems by lattice and superlattice design. First\, we discuss impro
vements in the realization of the kagome lattice model in materials with re
duced inter-kagome-layer coupling\, including observation of both the massl
ess and infinitely massive electronic bands expected therein. Second\, we
describe recent progress in realizing clean-limit 2D superconductivity in n
atural superlattice materials\, which potentially connect to models for fin
ite-momentum pairing and topological superconducting states. We comment on
the perspective for realizing further toy model systems in complex materia
l structures.
Host: J. Paglione
Refreshments 1:30pm John S
Toll Physics Bldg Room 1117
LAST-MODIFIED:20200128T154428Z
LOCATION:Room 1201 of the John S. Toll Building
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: Joe Checkelsky\, Massachusetts Institute of Technol
ogy
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180503T140000
DTEND;TZID=America/New_York:20180503T153000
DTSTAMP:20260524T204340Z
UID:22r21gjql8i94olaocj1sr2uso@google.com
RECURRENCE-ID;TZID=America/New_York:20180503T140000
CREATED:20170424T201551Z
DESCRIPTION:SPEAKER: Manuel Houzet\, CEA France\n\nTitle: Andreev and Majo
rana Weyl crossings in multi-terminal Josephson junctions\n\nAbstract: We a
nalyze the Andreev spectrum in a four-terminal Josephson junction between c
onventional and topological superconductors. We find that a topologically p
rotected crossing in the space of three superconducting phase differences c
an occur between the two Andreev bound states with lower energy. We discuss
the possible detection of this crossing through the nonlocal conductance q
uantization between two voltage-biased terminals.\n\nHOST: Jay Deep Sau
LAST-MODIFIED:20180420T140559Z
LOCATION:Toll Room 1201
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Manuel Houzet\, CEA France
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210218T140000
DTEND;TZID=America/New_York:20210218T153000
RRULE:FREQ=WEEKLY;WKST=SU;UNTIL=20201202T045959Z;BYDAY=TH
DTSTAMP:20260524T204340Z
UID:08j3n73ftaq1ntkpgvc7f5ask0@google.com
CREATED:20210125T181344Z
DESCRIPTION:Speaker: Matthew S. Foster\, Rice University\n\nTitle: TBA\nAbs
tract:\n\n\nHost: Anlage\nFor the zoom link please email Kristin Stenson at
QMC@umd.edu
LAST-MODIFIED:20210225T161650Z
LOCATION: Online via Zoom
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: Matthew S. Foster\, Rice University
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20250410T180000Z
DTEND:20250410T233000Z
DTSTAMP:20260524T204340Z
UID:4e02lhf291vjm2ffc3563ko46p@google.com
CREATED:20250407T135001Z
DESCRIPTION:Hybrid Superconductor-Semiconductor Materials Systems for Qu
antum Computing Applications
Title: TBA
Abstract:
Host
: TBA
Password: \;&nb
sp\; 558484
Host: Aaron Sternbach
Refreshments
at 1:30 pm - 1117 John S. Toll Bldg
LAST-MODIFIED:20250903T173659Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM - Mengkun Liu\; Stony Brook University
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20150416T140000
DTEND;TZID=America/New_York:20150416T153000
DTSTAMP:20260524T204340Z
UID:q985v6uteua502t37rg0nfh3ok@google.com
RECURRENCE-ID;TZID=America/New_York:20150416T140000
CREATED:20150115T203357Z
DESCRIPTION:SPEAKER: Prof. Carlo Beenakker\, Leiden\n\nTITLE: Electrical de
tection of the thermal quantum Hall effect\n\nABSTRACT: Two-dimensional su
perconductors with broken time-reversal symmetry have\nbeen predicted to su
pport chiral edge states\, providing a thermal\nanalogue of the electrical
quantum Hall effect in semiconductors.\nSeveral decades of search for these
edge states (notably in strontium\nruthenate) have not yet produced convin
cing evidence for their\nexistence. The key difficulty is that the edge sta
tes are charge\nneutral\, and therefore would seem to be out reach of conve
ntional\nelectrical probes. Here we discuss some recent developments in our
\nunderstanding of the Majorana nature of the superconducting edge states\,
\nwhich suggests that shot noise measurements would provide for a purely\ne
lectrical method of detection.\n\nHOST: Chris Lobb
LAST-MODIFIED:20150406T145913Z
LOCATION:Phys. Rm 1201
SEQUENCE:3
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Carlo Beenakker\, Leiden
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210204T140000
DTEND;TZID=America/New_York:20210204T153000
DTSTAMP:20260524T204340Z
UID:3km9k8ov7b5dbdq2o5h7eu14it@google.com
RECURRENCE-ID;TZID=America/New_York:20210204T140000
CREATED:20210122T134123Z
DESCRIPTION:Speaker: You Zhou\, UMD
Title: \;Wigner \;cry
stals \;in atomically thin heterostructures
Abstract:
A&n
bsp\;Wigner \;crystal \;is one of the earliest predicted collective
electronic states and exhibits intriguing quantum and classical phase tran
sitions. However\, realizing quantum \;Wigner \;crystals \;<
/u>requires placing semiconductors in a strong magnetic field\, limiting th
e detailed interrogation of these correlated states and their phase transit
ions. In this talk\, I will present a new platform to realize \;Wigner&
nbsp\;crystals \;without a magnetic field\, based on atomically
thin heterostructures made of transition metal dichalcogenides. In particul
ar\, we create semiconducting MoSe2 \;bilayers separated by
a thin insulating layer and electrically control the individual layer’s car
rier density. We observe optical signatures of a series of bilayer \;Wi
gner \;crystals \;formed at symmetric (1:1) and asymmetric (4:1 and
7:1) electron doping of the two MoSe2 \;layers. \;These bilayer \;Wigner \;crystals\, created from the commensurate
stacking of triangular electron lattices\, are remarkably stable and allow
us to probe both their quantum and classical melting transitions. These re
sults open up new avenues for creating and studying exotic many-body quantu
m phases in 2D systems.
Host: Paglione
Link: \;https://umd.zoom.us/j/91
Password: \; \; 558484
LAST-MODIFIED:20210204T191143Z
LOCATION: Online via Zoom
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: You Zhou\, UMD
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20180308T190000Z
DTEND:20180308T200000Z
DTSTAMP:20260524T204340Z
UID:iaiis0dikogv3fdq5o4ognk610@google.com
CREATED:20180118T033626Z
LAST-MODIFIED:20180308T193845Z
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:NO COLLOQUIUM THIS WEEK
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20190409T200000Z
DTEND:20190409T210000Z
DTSTAMP:20260524T204340Z
UID:5022iq6j83r5q3408oef9d0udl@google.com
CREATED:20190404T153718Z
DESCRIPTION:Carr Lecture\, to be held in 1412 John S. Toll Physics Building
\n\nSpeaker: Gregory S. Boebinger\, U.S. National High Magnetic Field Labor
atory and Florida State University and the University of Florida\n\nTitle:
Exploring the Heart of Quantum Matter with Extreme Magnetic Fields\n\nAbstr
act: In Quantum Matter\, intrinsic electronic charges and magnetic fields c
onspire in strange and weird ways to create new materials properties. High
magnetic fields are uniquely positioned to probe the mysteries that remain
at the heart of Quantum Matter\, where Nature creates 1/3 fractional electr
ic charges\, “spin liquids” of fixed charges but mobile magnetic fields\, a
nd high-temperature superconductivity in which the very existence of electr
ons as particles becomes suspect.
LAST-MODIFIED:20190404T153718Z
LOCATION:John S Toll Bldg\, Room 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:Carr Lecture: Gregory S. Boebinger
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220217T140000
DTEND;TZID=America/New_York:20220217T153000
DTSTAMP:20260524T204340Z
UID:7gbf8f9jj7hcki9dk68ao8ietv@google.com
RECURRENCE-ID;TZID=America/New_York:20220217T140000
CREATED:20220128T223503Z
DESCRIPTION:
Abstract: TBD
Host: TBD
\;
Location: Toll Physics Rm 1201
Seminar also on Zoom
Me
eting \;Link: \; \;https://umd.zoom.us/j/91301075848
[2] W. Braun et al.\,
APL Mater. 8\,071112 (2020)
[3] T. J. Smart\, J. Mannhart an
d W. Braun\, J. Laser Appl. 33\,022008 (2021)
[4] D. Y. Ki
m\, J. Mannhart and W. Braun\, APL Mater.9\, 081105(2021)
Host Aaron Sternbach
Refreshments at 1:30 pm - 1117 John S. Toll Bldg
LAST-MODIFIED:20250408T141801Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC Colloquium: Yinming Shao\, Pennsylvania State University
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20210506T140000
DTEND;TZID=America/New_York:20210506T153000
DTSTAMP:20260524T204340Z
UID:5srkfad2s905q6n3pl155k17ao@google.com
RECURRENCE-ID;TZID=America/New_York:20210506T140000
CREATED:20210129T165239Z
DESCRIPTION:Speaker: TBA
Title: TBA
Abstract:
Host
: TBA
Password: \; \;
558484
Abstract: Dielectric components play an integral role in the electr
onic communication\, navigation\, and defense systems\, all devices which u
nderpin daily life in our modern world. For many of these devices\, particu
larly those which are designed to operate in high-radiation environments li
ke space\, space-charging and resulting dielectric breakdown present a pers
istent and pressing challenge for long term functionality. However\, despit
e constituting a primary cause of failure for these materials\, the dynamic
s of dielectric breakdown in bulk dielectric materials are not well underst
ood. This is due in large part to the immense speeds at which these events
occur\, making it incredibly difficult to visualize. To systematically stud
y dielectric breakdown in dielectrics\, a novel optical delay line apparatu
s was developed for use in imaging this high-jitter\, extremely fast phenom
ena. The resulting images present the first-ever opportunity to undertake a
detailed analysis of the propagation dynamics of the dielectric breakdown
in poly-methylmethacrylate. The result of this work includes the identifica
tion of two distinct types of electrical tree formation\, including a previ
ously unreported classification. More significantly\, the propagation of th
is novel electrical tree type was observed to exceed ten million meters per
second and is believed to be the fastest physical phenomenon to ever be op
tically imaged in a solid material. The results of this analysis\, and the
ongoing work surrounding the characterization of charge loaded dielectric m
aterials will be presented.
HOST: JP
LAST-MODIFIED:20251103T174644Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM - Tim Koeth\, University of Maryland
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20171130T190000Z
DTEND:20171130T203000Z
DTSTAMP:20260524T204340Z
UID:p5p8tmcv6qrevi2cvson1p8i3g@google.com
CREATED:20170523T173806Z
DESCRIPTION:SPEAKER: Martin Sandberg\, IBM\n\nTITLE: Multi Qubit Quantum P
rocessors and the IBM Quantum Experience\n\nABSTRACT: In this talk I will
present a general overview of the quantum computing efforts at IBM. Hinging
on the development of high-quality superconducting quantum processors\, IB
M is aiming at building an ecosystem for quantum computing through the Quan
tum Experience. By providing cloud based access to real quantum hardware we
hope to sprue interest and accelerate the development of quantum computing
. Although the goal of a fault tolerant universal quantum computer is still
far away\, quantum computers might have an impact on certain problems (suc
h as quantum chemistry) on a much shorter time scale through approximate qu
antum computing. I will present our recently released 16 qubit processor an
d will discuss on some of the challenges related to building a multi-qubit
platform using superconducting hardware\, such as gate fidelities and deali
ng with crosstalk.\n\nHOST: Fred Wellstood\n\n
LAST-MODIFIED:20171127T021057Z
LOCATION:John S Toll Physics Bldg.\, Room 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Martin Sandberg\, IBM
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20240130T210000Z
DTEND:20240130T220000Z
DTSTAMP:20260524T204340Z
UID:2cfk2qae6gfhtv3g78m6ohpokr@google.com
CREATED:20231212T165012Z
DESCRIPTION:
Host: Frank Zhao
LAST-MODIFIED:20251104T195609Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:QMC Colloquium: Kin Fong\, Northeastern University
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART:20200326T180000Z
DTEND:20200326T190000Z
DTSTAMP:20260524T204340Z
UID:7qjtc5n16cgqo1onmtcb7lrc4p@google.com
CREATED:20191212T191111Z
LAST-MODIFIED:20200108T211209Z
LOCATION:Room 1201 of the John S. Toll Building
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM:
Abstract: \;The kagome lattic
e provides a fascinating playground to study geometrical frustration\, topo
logy and strong correlations. The newly discovered kagome metals AV3Sb5 (A=
K\, Rb\, Cs) exhibit various interesting phenomena including topological ba
nd structure\, symmetry-breaking charge density waves (CDWs) and supercondu
ctivity. Nevertheless\, the nature of the symmetry breaking in the CDW phas
e is not yet clear\, despite the fact that it is crucial to understand whet
her the superconductivity is unconventional. In this work\, we perform scan
ning birefringence microscopy and find that six-fold rotation symmetry is b
roken at the onset of the CDW transition temperature in all three compounds
. Spatial imaging and angle dependence of the birefringence show a universa
l three nematic domains that are 120◦ to each other. We propose staggered C
DW orders with a relative π phase shift between layers as a possibility to
explain the three-state nematicity in AV3Sb5. We also perform magneto-optic
al Kerr effect and circular dichroism measurements on all three compounds\,
and the onset of the both signals is at the CDW transition temperature\, i
ndicating broken time-reversal symmetry and the existence of the long sough
t loop currents in the CDW phase. Our work strongly constrains the nature o
f the CDWs and sheds light on possible unconventional superconductivity in
AV3Sb5.
Host: Johnpierre Paglione
\;
Seminar also
on Zoom
Meeting \;Link: \; \;https://umd.zoom.us/j/91301075848
Refreshments 1:30pm 1117 Toll Physics Bldg.
LAST-MODIFIED:20221004T150951Z
LOCATION:Toll Physics: Rm 1201
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC COLLOQUIUM: Liang Wu\, University of Pennsylvania
TRANSP:OPAQUE
ATTACH;FILENAME=QMC Colloquium_Oct 6_Liang Wu.pdf;FMTTYPE=application/pdf:h
ttps://drive.google.com/open?id=1-7ED6CgqtTB8pHW-3u3CO0ynTYVjb5ge&authuser=
0
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20180222T140000
DTEND;TZID=America/New_York:20180222T153000
DTSTAMP:20260524T204340Z
UID:22r21gjql8i94olaocj1sr2uso@google.com
RECURRENCE-ID;TZID=America/New_York:20180222T140000
CREATED:20170424T201551Z
DESCRIPTION:
SPEAKER: Nick Butch\, NIST
TITLE: \; Benea
th hidden order
\;ABSTRACT:
Host: Cheng Gong
R
efreshments at 1:30 pm - 1117 John S. Toll Bldg
LAST-MODIFIED:20260401T191313Z
LOCATION:1410 John S. Toll Bldg
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:QMC Colloquium: Bharat Jalan\; University of Minnesota
TRANSP:OPAQUE
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20170928T140000
DTEND;TZID=America/New_York:20170928T153000
DTSTAMP:20260524T204340Z
UID:22r21gjql8i94olaocj1sr2uso@google.com
RECURRENCE-ID;TZID=America/New_York:20170928T140000
CREATED:20170424T201551Z
DESCRIPTION:SPEAKER: Dr. Fahad Mahmood\, Johns Hopkins University\n\nTITLE
: “Locating the missing superconducting electrons in overdoped cuprates”\n\
nABSTRACT: High-Tc superconductivity in overdoped cuprates has been widely
believed to be within the standard Bardeen-Cooper-Schrieffer (BCS) paradigm
describing conventional superconductors. This view was strongly challenged
by recent measurements of the superfluid density which found that even as
the carrier concentration increases on the overdoped side\, the superfluid
density decreases – Cooper pairs seem to be ‘missing’ from the condensate.
Finding these ‘missing’ carriers and understanding why they fail to condens
e are crucial questions in explaining the superconducting transition in hig
h-Tc cuprates. In this talk I will discuss our recent measurements of the s
uperfluid stiffness in MBE grown films of the overdoped cuprate La2-xSrxCuO
4 over a broad frequency range (kHz to THz). By combining kHz range mutual
inductance measurements and time-domain THz spectroscopy on the same films\
, we track and quantify the distribution of carriers. In this way we direct
ly locate the “missing” carriers and discover that they display an exceedin
gly large metal-like response even deep into the superconducting state. An
analysis of this distribution in terms of a quantum Debye-Waller factor dem
onstrates the prominent role of quantum superconducting phase fluctuations
as the critical doping is approached.\n\nHost: Rick Greene
LAST-MODIFIED:20180420T140559Z
SEQUENCE:1
STATUS:CONFIRMED
SUMMARY:CNAM Colloquium: Dr. Fahad Mahmood\, Johns Hopkins University
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR