Influence of the van Hove singularity on the specific heat jump in BCS superconductors.pdf

2 0 0 2 p e S INFLUENCE OF THE VAN HOVE SINGULARITY ON 8 THE SPECIFIC HEAT JUMP IN BCS SUPERCONDUCTORS ] n o c TODOR MISHONOV,†,‡,∗ STEFAN-LUDWIG DRECHSLER§ and EVGENI PENEV‡ - † r Laboratorium voor Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven p Celestijnenlaan 200 D, B-3001 Leuven, Belgium u ‡Department of Theoretical Physics, Faculty of Physics, Sofia University “St. Kliment Ohridski” s 5 J. Bourchier Blvd., 1164 Sofia, Bulgaria . t §Institut f¨ur Festk¨orper- und Werkstofforshung Dresden, D-001171 Dresden, Germany a m - d Within the weak-coupling BCS scheme we derive a general form of the coefficients in n the Ginzburg-Landau expansion of the free energy of a superconductor for the case of a o Fermi level close to a van Hove singularity (VHS). A simple expression for the influence c of the VHS on the specific heat jump is then obtained for the case where gaps for different [ bands are distinct but nearly constant at the corresponding sheets of the Fermi surface. 1 v Keywords : Ginzburg-Landau theory, specific heat, gap anisotropy, van Hove singularity 2 9 1. Introduction 1 9 The influence of a van Hove singularity (VHS) on the properties of supercon- 0 1 2 duc