Field-Tuned Superconductor-Insulator Transition with and without Current Bias

The magnetic-field-tuned superconductor-insulator transition has been studied in ultrathin beryllium films quench condensed near 20 K. In the zero-current limit, a finite-size scaling analysis yields the scaling exponent product [Formula presented] and a critical sheet resistance, [Formula presented], of about [Formula presented], with [Formula presented]. However, in the presence of dc bias currents that are smaller than the zero-field critical currents, [Formula presented] becomes [Formula presented]. This new set of exponents suggests that the field-tuned transitions with and without a dc bias current belong to different universality classes. © 2002 The American Physical Society.