Orbital-selective two-gap superconductivity in kagome metal CsV3Sb5

Abstract: Recent experiments have revealed anisotropic multigap superconductivity in the kagome metal CsV3Sb5. However, the interplay between its multi-orbital character and electron-phonon coupling (EPC) in governing multiple superconducting gaps remains incompletely understood. In this work, we theoretically investigate the superconducting gap of CsV3Sb5 by combining first-principles calculations with superconducting density functional theory (SCDFT). Our results demonstrate that orbital-selective pairing drives the observed two-gap superconductivity in CsV3Sb5. Specifically, the two distinct gaps exhibit strong orbital dependence: a large, highly anisotropic gap (average magnitude ~0.64 meV) primarily originates from V-3d orbitals, while a small, isotropic gap (~0.25 meV) is associated with the Sb-5pz orbital. The V-3d orbitals strongly couple to the in-plane V-V bond-stretching and out-of-plane V-Sb bending phonon modes, whereas the kagome-plane Sb-5pz orbital weakly interacts with Cs shearing phonon mode. Moreover, our calculations reveal EPC-induced band renormalization, manifested as kinks at approximately -13 meV and -30 meV in the electronic dispersion, consistent with prior experimental observations. These findings provide fundamental insights into the orbital-selective superconductivity and EPC mechanisms in kagome CsV3Sb5.