EFFECT OF DISORDER ON CHARGE-DENSITY-WAVE AND SUPERCONDUCTING ORDER IN THE HALF-FILLED ATTRACTIVE HUBBARD-MODEL

The half-filled attractive Hubbard model exhibits a simultaneous charg e-density wave and superconducting order in its ground state. In this paper we use approximation-free quantum Monte Carlo techniques to expl ore the effect of disorder in the site energies on this degeneracy. We find that superconducting order survives randomness out to a critical amount of disorder, but charge ordering is immediately destroyed. Thi s settles the issue as to whether disordered site energies, which do n ot break time-reversal invariance, can destroy pairing correlations. W e also locate the precise ratio of disorder to bandwidth required for the disorder-driven transition from the superconducting state. We expl ore the validity of a strong-coupling picture which maps the system on to a Heisenberg model in a random magnetic field.