Tail states in clean superconductors with magnetic impurities
  We analyse 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. 
A. V. Shytov, I. Vekhter, I. A. Gruzberg, A. V. Balatsky