Title:Field induced phenomena and multiple superconducting phases in novel spin-triplet superconductor UTe2
Abstract: We present our results on the novel spin-triplet superconductor UTe2 discovered recently by S. Ran. UTe2 is a paramagnetic heavy fermion compound, which might be located at the proximity of ferromagnetic order. The huge upper critical field exceeding the Pauli limit is suggestive of the spin-triplet state. For the field along b-axis, the field reentrant superconductivity is observed up to Hm~35T, at which the first order metamagnetic transition occurs together with the enhancement of the effective mass. The field reentrant superconductivity in UTe2 is similar to those observed in ferromagnetic superconductors, namely URhGe and UCoGe. Applying the pressure in UTe2, the superconducting transition temperature splits and the multiple superconducting phase is detected as a thermodynamic response. When the field is applied along the easy a-axis, Hc2 abruptly increases at low temperature and high field region, as a consequence of multiple superconducting phases with different order parameters. We overview the results on UTe2 comparing with ferromagnetic superconductors, and present our perspective.