Theory of the isotope effect and superconducting transition temperature in high-T_c oxides

摘要

Analytical expressions for the superconducting transition temperature T_c and the isotope coefficient α have been obtained for the case where the Fermi level is close to the van Hove singularity. In this approach, we consider two interactions, the first related to the phonons and the second relevant to the magnetic excitations. Our result shows that the isotope coefficient α decreases with the superconducting transition temperature T_c in qualitative agreement with experimental data.