Dynamical effects on superconductivity in a BCS-BEC crossover: Dynamical mean field theory and numerical renormalization group study of the Holstein model in infinite dimensions

摘要

We investigate the dynamical effects of pairing interaction on superconductivity in BCS-BEC crossover by studying the Holstein model at half filling where the electron-phonon coupling g controls the crossover. The dynamical mean-field theory was employed in combination with the numerical renormalization group technique to study the frequency dependence of phonon mediated interaction between electrons in a superconductive state. The frequency dependence induces distinct features such as the absence of the dispersion back bending of Bogoliubov quasiparticles, nonmonotonous coupling dependence of the pairing gap, and the critical temperature T-c being maximum at g(c1), the lower critical coupling of the normal state insulator to metal transition. Some of these features have intriguing similarities with the recent observations in the FeSe1-xSx and Fe1+ySexTe1-x iron chalcogenides in the BCS-BEC crossover.