Superconductivity induced by impurities

The effect of impurities on the properties of a system with competing superconductive and dielectric transitions of the Peierls type is studied. The case is considered when in the absence of impurities the system would be a dielectric. It is shown that under three-dimensional conditions a sufficiently high impurity level induces a transition to the superconductive state. At a certain concentration the superconductive parameter is maximal. Further increase of the concentration destroys the superconductivity and restores the dielectric properties. Some arguments are presented which indicate that in one or two dimensions impurities do not induce superconductivity. The possibility of applying the present model to superconductivity in the organic superconductor (TMTSF)2ClO4 is discussed