Influence of nonmagnetic admixture on superconductivity in two-zone systems with variable density of charge carriers

By perturbation theory the analytical expressions for the temperature of the superconductivity transition $T_C$ and order parameters $\Delta _n$ ($n=1,2$) under different values of density of charge carriers (chemical potential $\mu$) are obtained for two-zone superconductors with nonmagnetic admixture. When admixture is input two mechanisms of its influence on $T_C$ and $\Delta _n$ are possible: the change of $\mu$ and the appearance of interzone scattering on the admixture potential. These mechanisms can compensate each other or both promote the destruction of superconductivity. This essentially depends on the role played by the factor of filling the energy zones due to which superconductivity can be completely suppressed by a nonmagnetic admixture.