Numerical analysis of the magnetic-field-tuned superconductor-insulator transition in two dimensions

Ground state of the two-dimensional hard-core-boson model subjected to exte rnal magnetic field and quenched random chemical potential is studied numer ically. In experiments, magnetic-field-tuned superconductor-insulator trans ition has already come under through investigation, whereas in computer sim ulation, only randomness-driven localization (with zero magnetic field) has been studied so far: The external magnetic field brings about a difficulty that the hopping amplitude becomes complex number (through the gauge twist ), for which the quantum Monte-Carlo simulation fails. Here, we employ the exact diagonalization method, with which we demonstrate that the model does exhibit field-tuned localization transition at a certain critical magnetic field. At the critical point, we found that the DC conductivity is not uni versal, but is substantially larger than that of the randomness-driven loca lization transition at zero magnetic field. Our result supports recent expe riment by Markovic et al. reporting an increase of the critical conductivit y with magnetic field strengthened. (C) 2001 Elsevier Science B.V. All righ ts reserved.