Thermodynamic evidence for a density-of-states peak near the Fermi level in YBa2Cu3O7-y

Thermodynamic properties such as the specific-heat discontinuity at the transition temperature (Tc), ΔC/Tc, and the zero-temperature critical field, Hc(0), of oxygen-deficient YBa2Cu3O7-y are analyzed to show that, within the framework of the BCS formalism, the density of states (DOS) at the Fermi level is peaked at y=0. The energy dependence of the DOS is considered for several models and found to be consistent with the Fermi level lying close to a two-dimensional van Hove singularity. © 1992 The American Physical Society.