Gap-to-Tc ratio as a function of the Fermi level shift

Abstract

Within the framework of the BCS theory, the gap-to-Tc ratio R = 2Δ0/kTc is evaluated numerically (Δ0 is the energy gap at T=0 and Tc is the critical temperature) for a superconductor with a van Hove singularity (vHs) in the density of states as a function of the shifts (δ) of the Fermi level with respect to the vHs. It is found that R varies asymmetrically with δ and that the variations are strong near δ = 0. Our numerical calculation shows that the largest R's occur at certain values of δ ≠ 0. © 1997 Plenum Publishing Corporation.