Density of States in the Energy Gap in the Superconducting Transition Metal Alloy

Abstract
For a model introduced in a preceding paper for the binary alloy of superconducting transition metals, the density of states is investigated. In the case of single impurity, the bound state is shown to appear in the energy gap if and only if the intraatomic Coulomb repulsion is stronger in the impurity atom than in the host atom. In the case of the finite concentration, it is shown both in the c-linear and the coherent potential approximations that this bound state broadens and constitutes the impurity band in the energy gap if the Coulomb repulsion is stronger in the impurity atom. If the Coulomb repulsion is weaker in the impurity, on the other hand, the impurity band is shown not to appear in the energy gap.

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