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 and treating the order parameter self-consistently we show that the density of states is finite everywhere in the superconducting gap, and that it varies as $\ln N(E)\propto -|E-{\Delta }_0{|}^{(7-d)/4}$ near the mean field gap edge ${\Delta }_0$ in a $d$-dimensional superconductor. In contrast to most studied cases the optimal fluctuation is strongly anisotropic.

• Received 10 June 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.147002