Saddle-point pairing: an electronic mechanism for superconductivity

Abstract

It is shown that the interactions in a strongly correlated quasi-two-dimensional electron gas with the Fermi level lying at a saddle point (Van Hove singularity) in ε_k can give rise to superconductivity by exchange of excitations with a characteristic low electronic energy scale E^∗. Application to cuprate superconductors shows that this mechanism along with a conventional electron-phonon interaction can explain the high T_c's and the anomalous behavior of the isotope shift as a function of doping.