Crossover between electron-electron and electron-phonon mediated pairing on the Kagome lattice

We study electron-electron and electron-phonon mediated pairing in the Holstein extended Hub- bard model on the Kagome lattice at the van Hove fillings, and investigate the competition and cooperation between the two pairing mechanisms. We find that electron-phonon and electron- electron pairing are cooperative in a crossover region, where the two pairing mechanisms are of comparable strength and where the filling is close to a van Hove singularity. In particular, at the p-type van Hove filling the two pairing mechanisms are cooperative in the E_1u (p-wave) and B_2u (f_y3−3yx2-wave) channels, whereas at the m-type van Hove filling they are cooperative in the E_1u channel, but weakly competitive in the B_2u channel. Moreover, we show that the electron-phonon interaction acquires a significant momentum dependence, due to the sublattice texture of the Fermi surfaces, which can promote non s-wave pairing. We present a detailed analysis of these pairing propensities and discuss implications for the vanadium-based kagome superconductors AV3Sb5.