Interaction-induced Bose metal in two dimensions

We show here that the regularization of the conductivity resulting from the bosonic interactions on the "insulating" (quantum-disordered) side of an insulator-superconductor transition in two dimensions, gives rise to a metal with a finite conductivity, σ= (2/π)4e²/h, as temperature tends to zero. The Bose metal is stable to weak disorder and hence represents a concrete example of an interaction-induced metallic phase. The phenomenological inclusion of dissipation reinstates the anticipated insulating behavior in the quantum-disordered regime. Hence, we conclude that the traditionally studied insulator-superconductor transition, which is driven solely by quantum fluctuations, corresponds to a superconductor-metal transition. The possible relationship to experiments on superconducting thin films in which a low-temperature metallic phase has been observed is discussed.