GAP ENERGY, ISOTOPE EFFECT AND COHERENCE LENGTH IN HIGH Tc-OXIDES

Abstract

The model recently developed by Getino et al. to study the gap energy in the van Hove scenario in high-T c oxides is extended to study the isotope effect and the coherence length in these materials. We propose a more realistic model by: (1) adding a constant term to the singular logarithmic contribution, within the weak coupling BCS theory and a phonon mediated interaction; (2) assuming the Fermi level lies close to a van Hove singularity for optimal doping. The equations obtained from this approach, are applicable to low as well as high temperature superconductors successfully the superconducting temperature transition T c , the gap energy Δ, the isotope effect α and the coherence length ξ. For high-T c oxides, it is found that when the effective mass of carriers tends to be large, α and ξ tend to be small where T c and Δ became larges. We shown that when the effective mass of carriers is enclosed between 5 m e and 15 m e , the values obtained for these parameters are in agreement with experimental data.