INFLUENCE OF NONMAGNETIC IMPURITIES ON SUPERCONDUCTIVITY IN 2-BAND SYSTEMS WITH VARIABLE CHARGE-CARRIER DENSITIES

Two-band superconductors with a nonmagnetic impurity are considered in the framework of perturbation theory. Analytical expressions are obta ined for the temperature of the superconductivity transition T-C and t he order parameters Delta(n) (n = 1, 2) at different values of the cha rge carrier density (chemical potential mu). An impurity introduced in to the system can influence T-C and Delta(n) in two ways: it can lead to a change in mu and can cause inter-band scattering by the impurity potential. These mechanisms can either cancel each other or destroy th e superconductivity. Here a significant role is played by the occupati on of the energy bands, by which superconductivity can be completely s uppressed by the nonmagnetic impurity.