Large Oscillatory Thermal Hall Effect in Kagome Metals
The thermal Hall effect is a powerful tool for probing the exotic nature of correlated quantum matter. As the thermal analog of the electrical Hall effect, it detects a transverse temperature gradient in the presence of a longitudinal heat current and a perpendicular magnetic field. Unlike its electrical counterpart, the thermal Hall effect is more universal, arising from the chirality of carriers, whether they are charged particles like electrons or neutral excitations such as phonons, magnons, or more exotic quasiparticles.
While unconventional thermal Hall effects have offered valuable insights into correlated quantum systems, a significant challenge lies in determining whether a thermal Hall signal originates from fermionic or bosonic carriers. A key breakthrough was the observation of quantum oscillations (QOs) in the thermal conductivity of α-RuCl₃. These QOs, resulting from Landau level quantization, suggest a fermionic response and offer a promising avenue for distinguishing between fermionic and bosonic contributions. Analyzing the temperature dependence of these oscillations in thermal conductivity can further confirm their origin and validate the underlying mechanisms.
However, detecting OQs in thermal conductivity and thermal Hall effect is challenging due to their typically small magnitude. To enhance sensitivity, we developed a differential amplifier technique, achieving a transverse temperature resolution of 0.01 mK. Using this method, we measured the thermal Hall effect in the Kagome metal CsV₃Sb₅ and observed QOs for the first time in a quantum correlated material. Notably, the low-temperature oscillation amplitude of the thermal Hall conductivity was 2.5 times larger than the corresponding electrical Hall conductivity oscillation amplitude scaled by the Sommerfeld value L 0 T. This strong violation of the oscillatory Wiedemann-Franz law suggests the presence of an exotic correlated quantum phase.