Magnetotransport properties near the superconductor-insulator transition in two dimensions

Abstract

We analyze here the behavior near the two-dimensional insulator-superconductor quantum critical point in the presence of a perpendicular magnetic field. We show that with increasing field H, the quantum disordered and quantum critical regimes, in which vortex degrees of freedom are suppressed, crossover to a new magnetically activated (MA) regime, where the correlation length $\ensuremath{\xi}\ensuremath{\sim}1/\sqrt{H}.$ In this regime, we show that the conductivity decreases monotonically as opposed to the anticipated saturation predicted from hyperuniversality arguments. This discrepancy arises from the lack of commutativity of the frequency and temperature tending to zero limits of the conductivity. In the low-field regime such that $\sqrt{H}\ensuremath{\ll}\ensuremath{\Delta},$ and in the absence of Ohmic dissipation, where $\ensuremath{\Delta}$ is a measure of the distance from the quantum critical point, the resistivity saturates to the Bose metal value found previously for Cooper pairs lacking phase coherence.