Tail states in superconductors with weak magnetic impurities

Abstract We analyze the behavior of the density of states in a singlet s-wave superconductor with weak magnetic impurities in the clean limit by using the method of optimal fluctuation. We show that the density of states varies as ln N(E)∝−|E−Δ 0 | (7−d)/4 near the mean field gap edge Δ0 in a d-dimensional superconductor. The optimal fluctuation in d>1 is strongly anisotropic. We compare the density of states with that obtained in other recent approaches.