Isotopic mass and pressure dependent changes for extended s-wave superconductors

Abstract

We consider a tight-binding model comprising a hopping and an attractive interaction term to obtain superconductivity. Exact expressions for the isotope-shift exponent and the pressure coefficient of transition temperature are derived invoking the isotopic mass and pressure dependence of both the hopping and attractive interaction terms. The variations of and are studied as a function of the chemical potential and the transition temperature. With proper choice of parameters we obtain large positive values of for low- samples and a minimum in near optimum doping. It is found that is large and positive for low- underdoped systems and small near optimum doping. These results qualitatively agree with the experimental results of hole-doped high- oxides. The behaviour of for electron-doped oxide systems can also be explained from the model.