Observation of time-reversal symmetry breaking under charge density wave of CsV₃Sb₅ by circular dichroism ARPES

Jaehun Cha

     The layered vanadium-based Kagome metals AV₃Sb₅ (A=K, Rb, Cs) have attracted a large attention in recent topological material studies. In particular, the charge density wave (CDW) of this material is related not only with superconductivity, but also non-trivial topology of band structure [1]. In anomalous Hall transport and scanning tunneling microscopy studies, the chiral and time-reversal symmetry breaking in the charge ordering has been reported, and the broken symmetry in the CDW generates the non-vanishing Berry curvature along the non-trivial band topology [2, 3]. However, the Berry curvature in detailed electronic band structure has not been examined experimentally, although it is required to understand the relationship between CDW and band topological nature.

     In this presentation, we report a Berry curvature distribution and its temperature dependence in layered Kagome metal CsV₃Sb₅ by circular dichroism angle-resolved photoemission spectroscopy (CD-ARPES). Analyzing the symmetry of electronic structure and effect of experimental geometry [3], we extract the Berry curvature in our CD-ARPES results. Notably, the measured Berry curvature and its integration follow the CDW phase transition, and they are vanished at higher temperature above CDW transition temperature. Our work implies that CDW phase in CsV₃Sb₅ has time-reversal symmetry breaking nature and it is observed as the Berry curvature in electronic band structure. In addition, we also observe a time-reversal symmetry breaking in CDW phase on the van Hove singularity as well as on the Dirac nodal line of band structure. 

[1] M. Kang et al., Nat. Phys. 18, 301-308 (2022)

[2] F. H. Yu et al., Phys. Rev. B, 104, L041103 (2021)

[3] Y. -X. Jiang et al., Nat. Mater. 20, 1353-1357 (2021)

[4] S. Cho et al., Phys. Rev. Lett. 121, 186401 (2018)