Concentration dependence of the transition temperature and isotope-effect exponent in high-Tc superconductors
Pashitski E. A.
The nonmonotonic concentration dependence which has been observed experimentally for the transition temperature Tc and the oxygen isotope-effect exponent a0 can be explained by the model of a "plasmon" mechanism for superconductivity in a layered metal with a narrow 2D band near the Fermi level. The reasons are that this mechanism is invariant under a change in the sign of the charge carriers and that the plasma frequency of the "heavy" carriers is a nonmonotonic function of the extent to which the narrow band is filled. A possible explanation is proposed for the positive sign of the derivative of Tc with respect to the pressure in the new compound HgBaCaCuO with Tc> 130 K.