Nonlinear optical spectroscopy studies of a Kagome lattice material RbV₃Sb₅

The transition-metal Kagome lattice materials provide an exciting platform to investigate the quantum interactions among electron correlation, topology, and geometric frustration. The recently discovered Kagome superconductors AV₃Sb₅ (A=K, Rb, Cs) with nontrivial topological band structures and multiply intertwined broken symmetry states have attracted tremendous research interest. A charge density wave (CDW) order with broken time-reversal symmetry and other point group symmetries has been observed in AV₃Sb₅, which possible suggests the presence of a hidden ordered state and yet awaits comprehensive understanding. Optical second-harmonic generation (SHG), a doubling frequency generation process by nonlinear light-matter interactions inside the material of interest, can directly probe point group symmetry changes across phase transitions and therefore has been used to search for otherwise hidden orders. In this talk, I will present our results on the Kagome superconductor RbV₃Sb₅ measured by rotation anisotropy (RA) SHG. I will particularly focus on the temperature dependence of RA SHG that reveals the full point group symmetry evolutions in RbV₃Sb₅ across various transition temperatures.