Role of Van Hove singularity in high-temperature superconductors: Mean field

Abstract

Realistic U= models, for oxide superconductors are solved in slave-boson mean-field approximation. A successful understanding is achieved of the paramagnetic susceptibility and specific heat, the energy dispersion seen in photoemission, the shape and topology of the Fermi surface, the relative weights of copper and oxygen both in NMR and photoemission spectroscopies and the observed energy gaps in the p- and n-type materials. The Fermi level is found to lie very close to the nearly logarithmic van Hove singularity in the density of states over a substantial range of doping. This makes it possible without large Fermi-liquid parameters to reconcile the light mass found in photoemission experiments with the high density of states deduced from thermodynamic data. Further important consequences for the behavior of the imaginary part of the self-energy and for pairing mechanisms are outlined. © 1991 The American Physical Society.