Mechanism of even- and odd-parity density-waves and beyond-Migdal superconductivity in kagome metal AV₃Sb₅ (A = K, Rb, Cs)

Exotic quantum phase transitions in strongly correlated metals have been discovered one after another and found to be universal now. The multistage unconventional density-wave (DW) orders in frustrated kagome metal AV₃Sb₅ and its interplay with exotic superconductivity attract increasing attention. We find that the time-reversal symmetric star-of-David bond-order originates from sizable intersite attraction due to the quantum interference among paramagnons [1]. This mechanism is important in kagome metals because the geometrical frustration prohibits the freezing of paramagnons. In addition, we uncover that moderate bond-order fluctuations mediate sizable pairing glue, and this mechanism gives rise to both singlet s-wave and triplet p-wave superconductivity [1]. The obtained impurity-induced change in the SC state is consistent with recent experiments [3]. Furthermore, we discovered that the time-reversal broken charge current order is naturally caused by the bond-order fluctuations [4]. Interestingly, the coexistence of the charge-current order and the bond-order gives rise to a novel nematic state [4]. Thus, both the exotic density waves and the superconductivity in geometrically frustrated kagome metals are explained by the quantum interference mechanism.