Cascade of symmetry-broken electronic phases in kagome superconductors AV₃Sb₅

The kagome lattice of transition metal atoms provides an exciting platform to study the interplay of electronic correlations and band topology. Recently discovered non-magnetic kagome metals AV₃Sb₅ (A=K, Rb, Cs) set off an avalanche of theoretical and experimental work as rare superconductors in the kagome structure. Experiments uncovered numerous exotic electronic phenomena in these materials, including novel density waves, topological surface states, time-reversal symmetry breaking and potentially unconventional superconductivity. In this talk, I will discuss our experiments on AV₃Sb₅ where we uncovered a cascade of symmetry-broken electronic states emerging as the material is cooled down. Using variable-temperature spectroscopic imaging scanning tunneling microscopy, we first detect a high-temperature tri-directional charge order with a 2a₀ period that breaks the translation symmetry of the lattice. As the system is cooled down towards the superconducting transition, we observe an additional breaking of the six-fold rotation symmetry, which persists through the superconducting transition. This rotation symmetry breaking is reflected in the emergence of an additional 4a₀ charge-stipe order and strongly anisotropic coherent quasiparticles related to the kagome Vanadium bands. Our experiments reveal a complex landscape of electronic states that can co-exist on a kagome lattice, and provide intriguing parallels to high-T_c superconductors and twisted bilayer graphene.