Density of states of a d-wave superconductor in the presence of strong impurity scatterers:: A nonperturbative result

We present a method to compute the density of states induced by a finite density of nonmagnetic impurities in a d-wave superconductor, in the unitary limit of very strong scattering centers. For frequencies very small as compared to the superconducting gap (omega much less than Delta (0)) the additional density of states has the leading divergence delta rho(omega)similar or equal ton(i)/(\2 omega \ln(2)\omega/Delta (0)\). This result is nonperturbative.