Dependence of the Gap-Ratio on the Fermi Level Shift in a Van Hove Superconductor

Abstract

To understand the origin of high temperature superconductivity model based on the close proximity of the Fermi level to a quasi-two-dimensional Van Hove Singularity (VHS) in the density of states has been suggested. Here we present our study of the dependence of the zero temperature gap to the critical temperature for s-and d-wave superconductors on the Fermi level shift (δ) from the VHS within the BCS theory. Exact numerical calculations for the s and d gap ratios are carried out and approximate analytic expressions for the ratio are given. We find that the maximum gap ratio occurs at δ = 0, and it decreases symmetrically with increasing δ.

Fundamental Properties and Origin of the High-Tc Cuprate Superconductors: Development of Concepts

“…The large value of this parameter is still not understood. Various approaches based on electronic as well as phononbased interaction, sometimes for isotropic s-wave and other times for d-wave pairing, have been proposed to explain the large value of R [95,[98][99][100][101][102][103][104][105] but the maximum values of this parameter are still much lower than the experimental results.…”