Phonon-mediated s-wave superconductivity in the kagome metal CsV3Sb5 under pressure

The nature of the superconducting pairing state in the pristine phase of the compressed kagome metal CsV3Sb5 under pressure is studied by the Migdal-Eliashberg formalism and density-functional theory calculations. We find that the superconducting gap distribution driven by electron-phonon coupling is anisotropic and nodeless. It is revealed that the V 3d and Sb 5p orbitals forming the four Fermi surface sheets are strongly coupled to the V-V bond-stretching and V-Sb bond-bending phonon modes. The resultant superconducting gaps associated with V 3d(xy,x2_y2,z2) and 3d(xz,yz) orbitals is larger in their average magnitude and more widely spread compared to that associated with the Sb 5pz orbital. Meanwhile, we find that unconventional superconductivity driven by electron correlation effects is unlikely because the saddle points at the M point near the Fermi level do not generate van Hove singularities in the total density of states. Our findings demonstrate that the superconductivity of compressed CsV3Sb5 can be explained by the anisotropic multiband pairing mechanism with conventional phonon-mediated s-wave symmetry, evidenced by recent experimental observations at ambient pressure and under pressure.