Scanning time-resolved optical studies on Kagome superconductors

The kagome lattice provides a fascinating playground to study geometrical frustration, topology and strong
correlations. The newly discovered kagome metals AV_3Sb_5 (A = K, Rb, Cs) exhibit exotic phases including
charge density waves (CDWs) and superconductivity. In our study, we perform scanning birefringence and circular
dichroism (CD) microscopy on CsV_3Sb_5. The scanning birefrigence demonsate six-fold rotational symmetry
breaking in the CDW phase and three domains that are 120 degree to each other. The emergence of opposite CD
domains within the same birefringence domain, along with field-induced CD switching, indicate broken time-reversal symmetry. Furthermore, ultrafast pump-probe reflectivity measurements reveal a splitting of charge density wave induced phonon modes in all three birefringence domains. Such a breaking in degeneracy corroborates the six-fold rotation symmetry breaking in the charge ordered phase. I will also discuss the CDW fluctuations from the pump-probe measurement.