LOWER-BOUND FOR THE FERMI-LEVEL DENSITY-OF-STATES OF A DISORDERED D-WAVE SUPERCONDUCTOR IN 2 DIMENSIONS

We consider a disordered d-wave superconductor in two dimensions. Rece ntly, we have shown in an exact calculation that for a lattice model w ith a Lorentzian distributed random chemical potential the quasipartic le density of states at the Fermi level is nonzero; As the exact resul t holds only for the special choice of the Lorentzian, we employ diffe rent methods to show that for a large class of distributions, includin g the Gaussian distribution, one can establish a nonzero lower bound f or the Fermi-level density of states. The fact that the tails of the d istributions are unimportant in deriving the lower bound shows that th e exact result obtained before is generic. [S0163-1829(98)01617-8].