Analysis of the superconducting transition temperature's pressure dependence for YBa 2Cu 3O 7−δ within a BCS framework

Abstract

The pressure dependence of the superconducting transition temperature d T c/d P of the YBa 2Cu 3O 7 high- T c superconductor is addressed. A value of dln T c/dln V (where V is the volume) comparable to the phonon Grüneisen parameter is revealed, thereby allowing for reasonable analysis using the Allen-Dynes equation for T c. The electronic contribution to the electron-phonon coupling parameter η is found to be positively influenced by pressure, with a volume dependence of dln η/dln V ≈ −3, and to offset the Grüneisen parameter's contribution in the equation for dln T c/dln V by about a factor of 1.5 thus resulting in a positive pressure dependence of T c. This value is comparable to that observed in conventional superconductors. The possible influence of a van Hove singularity near the Fermi energy on T c( P) results is discussed.