Universal conductivity of dirty bosons at the superconductor-insulator transition

The superconductor-insulator transition at zero temperature in two dimensions is studied by Monte Carlo simulations of interacting bosons (Cooper pairs) moving in a quenched random potential. We calculate the universal conductivity σ* and the critical exponents at the superconductor-insulator transition. For the short-range repulsive case we find σ*=(0.14±0.03)σQ, where σQ-1==RQ ==h/(2e)2≃6.45kΩ, and for long-range Coulomb interactions we find σ*=(0.55±0.1)σQ.