ÖPG-CMD Joint Meeting 2026

Observation of Anomalous Thermal Hall Effect in a Kagome Superconductor CsV3Sb5

Sep 23, 2026, 10:30 AM

30m

HS 15.14 (University of Graz)

4) Invited talk M02 - Heavy quasiparticles in heavy fermion compounds Mini-Colloquium

Speaker

Minoru Yamashita (ISSP, University of Tokyo)

Description

Spontaneous time-reversal symmetry (TRS) breaking is one of the interesting cooperative phenomena brought by a phase transition in solids, which allows both a spontaneous magnetic moment as observed in a ferromagnet and a chiral edge flow to be realized. Of particular interest in the chiral flow by the broken TRS is the topologically-protected edge current in a chiral superconductor in which spontaneous magnetic moment appears by forming Cooper pairs with a finite orbital angular momentum. In contrast, conventional superconductivity is incompatible with collective magnetism and broken TRS. Although a charge current is not conserved in a superconductor, a thermal current brought by Bogoliubov quasiparticles is conserved, giving rise to a quantization of the thermal Hall conductivity in a chiral superconductor by the Chern number characterizing the chiral superconducting state. In addition to such an intrinsic anomalous thermal Hall effect (ATHE), extrinsic ATHEs by impurity scatterings are also suggested in chiral superconductors. Although numerous candidate materials have been reported so far to realize chiral superconductivity, mainly by the observation of the spontaneous magnetization by the polar Kerr or the μSR measurements, these ATHEs have yet to be observed.

In this presentation, I will report our successful observation of an ATHE developing below the superconducting transition temperature at zero external magnetic field in the kagome-lattice superconductor CsV₃Sb₅ [1]. The anomalous thermal Hall conductivity (κ_xy^ATHE) is determined by measuring the transverse temperature difference caused by a thermal current at zero external field, after cooling the sample under a finite magnetic field at the superconducting transition to polarize the domains of the chiral superconductor. Reversing this “training” field allows us to estimate κ_xy^ATHE by antisymmetrizing the transverse thermal-Hall resistance to remove the mixed longitudinal component. We verify our experimental setup by confirming the null result for the conventional type-II superconductor 2H–NbS₂. We further exclude the effects of trapped fluxes in the sample by measuring the training-field dependence of the trapped field by micro-Hall array measurements. Our results demonstrate that the magnitude of κ_xy^ATHE observed in CsV3Sb5 exceeds the theoretical value expected for an intrinsic ATHE of a chiral superconductor by more than one order of magnitude, as well as exhibits a different temperature dependence of κ_xy^ATHE from that of an intrinsic ATHE. On the other hand, both the magnitude and the temperature dependence of κ_xy^ATHE are consistent with an extrinsic impurity-induced ATHE that predicts a temperature dependence of κ_xy^ATHE with a peak at a fraction of the superconducting transition temperature without the residual of κ_xy^ATHE/T depending on the impurities, suggesting observation of extrinsic ATHE in a chiral superconducting state in CsV₃Sb₅. The method we use to observe the ATHE is applicable to various superconductors, which will bring substantial advances in the research on chiral superconductivity.

[1] H. Yoshida et al., Sci. Adv. 11, eadu2973 (2025)