Internal Transition of Superconducting State by Impurity Doping with a Jump of Isotope-effect Coefficient in Multiband Superconductors

Abstract

The impurity effects on the transition temperature T_c and the isotope effect are examined in multiband superconductors with magnetic and nonmagnetic impurities, where the effect of Coulomb repulsion is considered. It is shown that an internal transition of the superconducting state is induced by impurity doping, and that the transition is accompanied by a jump of the isotope-effect coefficient α. In particular, the transition is illustrated in a system with two electron bands. In some special cases, extended Abrikosov and Gor’kov (AG) equations for T_c and the expressions of the isotope-effect coefficient α are obtained. Possible relevance of the present mechanism to the experimental results of Sr₂RuO₄ is discussed.