Bose metal: Gauge-field fluctuations and scaling for field-tuned quantum phase transitions

We extend our previous discussion of the Bose metal to the field-tuned case. We point out that the recent observation of the metallic state as an intermediate phase between the superconductor and the insulator in the field-tuned experiments on MoGe films is in perfect consistency with the Bose metal scenario. We establish a connection between general dissipation models and gauge-field fluctuations and apply this to a discussion of scaling across the quantum phase boundaries of the Bose metallic state. Interestingly, we find that the Bose metal scenario implies a possible two parameter scaling for resistivity across the Bose metal-insulator transition, which is remarkably consistent with the MoGe data. Scaling at the superconductor-metal transition is also proposed, and a phenomenolgical model for the metallic state is discussed. The effective action of the Bose metal state is described and its low energy excitation spectrum is found to be ω∝k³.