On isotope effect in superconducting materials with singular energy spectra

The isotope mass effect in generalized BCS-like model of superconductor with singularities in energy spectrum is considered. The calculations are performed for logarithmic and square-root van Hove singularities corresponding to quasi-2D and quasi-1D systems. The effects of finite life-times of electronic states are taken into account by shifting the singularities off the rreal axis in the complex energy plane.