Tail states in superconductors with weak 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. We show that the density of states 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. The optimal fluctuation in d>1 is strongly anisotropic. We compare the density of states with that obtained in other recent approaches. 
I. Vekhter, A. V. Shytov, I. A. Gruzberg, and A. V. Balatsky