Two elementary band representation model, Fermi surface nesting, and surface topological superconductivity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi><mml:msub><mml:mi mathvariant="normal">V</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">Sb</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:math> (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi></mml:math> = K, Rb, Cs)
Junze Deng, Ruihan Zhang, Yue Xie, Xianxin Wu, Zhijun Wang
Abstract
The recently discovered vanadium-based Kagome metals $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}$ ($A=\text{K,}\phantom{\rule{4.pt}{0ex}}\text{Rb,}\phantom{\rule{4.pt}{0ex}}\text{Cs}$) 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 ${A}_{g}@3g$ ($\text{V}\text{\ensuremath{-}}{d}_{{x}^{2}\ensuremath{-}{y}^{2}/{z}^{2}}$, Kagome sites) and ${A}_{2}^{\ensuremath{''}}@2d$ EBRs (Sb1-${p}_{z}$, honeycomb sites). We have investigated the Fermi surface instability by calculating the electronic susceptibility $\ensuremath{\chi}(\mathbit{q})$. 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 $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2$ 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 ${\mathrm{FeTe}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x}$ 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.