No abstract

No abstract

No abstract

The model recently developed by Getino et al. to study the gap energy in the van Hove scenario in high-Tc 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 Tc, the gap energy ∆, the isotope effect α and the coherence length ξ. For high-Tc oxides, it is found that when the effective mass of carriers tends to be large, α and ξ tend to be small where Tc and ∆ became larges. We shown that when the effective mass of carriers is enclosed between 5 me and 15 me, the values obtained for these parameters are in agreement with experimental data.