From Loop-current Chern metal to pair density wave and higher-charge superconductivity in kagome superconductors AV₃Sb₅ (A=K, Cs, Rb)

The study of transition-metal kagome lattice materials has leapt forward with the recent discovery of superconductivity in vanadium-based nonmagnetic kagome metals AV₃Sb₅ (A=K, Cs, Rb). We overview the experimental evidence for possible time-reversal symmetry breaking charge density wave in the normal state, the novel pair density wave (PDW) in the superconducting state, and charge-4e and charge-6e superconductivity. We argue that the essential phenomenology can be captured by a doped orbital Chern insulator with staggered loop currents and Chern Fermi pockets carrying concentrated Berry curvature. Cooper pairing in the Chern metal can generate a roton PDW state characterized by an emergent vortex-antivortex lattice of loop-supercurrents. The possible realizations of higher-charge superconductivity and intrinsic chiral topological PDW superconductors will be discussed.