Abstract
Using Eliashberg theory and a model density for α2 F the transition temperatureT c and the isotope effect α are calculated near an extended van Hove singularity. We show that, at least in the one-particle and the Migdal approximation, even the considered strong van Hove singularity cannot yield large enhancements ofT c and strong reductions of α of the kind observed in experiment around optimal doping.
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