Two elementary band representation model, Fermi surface nesting, and surface topological superconductivity in AV3Sb5 (A = K, Rb, Cs)

The recently discovered vanadium-based Kagome metals AV3Sb5 (A = K, Rb, Cs) are of great interest with the interplay of charge density wave (CDW) order, band topology and superconductivity. In this paper, by identifying elementary band representations (EBRs), we construct a two-EBR graphene-Kagome model to capture the two low-energy van-Hove-singularity dispersions and, more importantly, the nontrivial band topology in these Kagome metals. This model consists of Ag@3g (V-dx2-y2/z2, Kagome sites) and A 2@2d EBRs (Sb1-pz, honeycomb sites). We have investigated the Fermi surface instability by calculating the electronic susceptibility chi(q). Prominent Fermi-surface nesting peaks are obtained at three L points, where the z component of the nesting vector shows an intimate relationship with the anticrossing point along M-L. The nesting peaks at L are consistent with the 2 x 2 x 2 CDW reconstruction in these compounds. In addition, the sublattice-resolved bare susceptibility is calculated and similar sharp peaks are observed at the L points, indicating a strong antiferromagnetic fluctuation. Assuming a bulk s-wave superconducting pairing, the helical surface states and nontrivial superconducting gap are obtained on the (001) surface. Analogous to the FeTe1-xSex superconductor, our results establish another material realization of a stoichiometric superconductor with nontrivial band topology, providing a promising platform for studying exotic Majorana physics in condensed matter.