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CsV₃Sb₅ is a quasi-2D metal where the V atoms make a kagome lattice. It has a charge density wave (CDW) order and two time reversal symmetry  breaking (TRSB) orders and is expected to have nontrivial Z₂ band topology [1]. We use a photo-thermal microscope for high resolution thermal diffusivity and optical differential reflectivity measurements in CsV₃Sb₅ by measuring phase delay in local reflectivity. This is supplemented with specific heat and Kerr effect measurements. Our primary observation is at the CDW transition, a strong anomaly is observed in thermal diffusivity. Within within eight degrees of the CDW transition temperature, there diffusivity plummets by 40%. Resistivity measurement data is used to extract the electronic contribution of thermal conductivity. We will further discuss various contributions to the thermal conductivity and validity of the Wiedemann–Franz law law.

[1] L. Yu, et al, arXiv:2107.10714