Quantum Monte Carlo study of the disordered attractive Hubbard model

We investigate the disorder-driven superconductor to insulator quantum phas e transition (SIT) in an interacting fermion model using determinantal quan tum Monte Carlo (QMC) methods. The disordered superconductor is modeled by an attractive Hubbard model with site disorder chosen randomly from a unifo rm distribution. The superconducting state which exists for small disorder is shown to evolve into an insulating phase beyond a critical disorder. The transition is tracked by the vanishing of (a) the superfluid stiffness, an d (b) the charge stiffness or the delta function peak in the optical conduc tivity at zero frequency. We also show the behavior of the charge, spin, pa ir, and current correlations in the presence of disorder. Results for the t emperature dependence of the de conductivity, obtained by an approximate an alytic continuation technique, an also presented both in the metallic phase above T-c and the insulating phase. We discuss some of the complications i n extracting the resistance at the transition point. [S0163-1829(99)00306-9 ].