Mechanism of exotic density-wave and beyond-Migdal unconventional superconductivity in kagome metal AV3Sb5 (A=K, Rb, Cs)

Exotic quantum phase transitions in metals, such as the nematic and smectic states, were discovered one after another and found to be universal now. The emergence of unconventional density-wave order in frustrated kagome metal AV${}_3$Sb${}_5$ and its interplay with exotic superconductivity attract increasing attention. We reveal that the smectic bond-density-wave is naturally caused by the paramagnon interference mechanism, because strong scatterings among different van-Hove singularity points are induced. In addition, the fluctuations of the bond-order induce sizable “beyond-Migdal” pairing glue, and therefore both singlet nodal $s$-wave pairing and triplet $p$-wave pairing states are expected to emerge. The coexistence of both states would explain exotic superconducting states. Unexpected similarities between kagome metal and some Fe-based superconductors are discussed. This study enables us to understand the exotic density wave, superconductivity and their interplay in kagome metals based on the interference mechanism.