Existence of a Bose metal at T=0

This paper aims to justify the existence of a two-dimensional Bose metal, i .e., a metallic phase made out of Cooper pairs at T=0. To this end, we cons ider the physics of quantum phase fluctuations in (granular) superconductor s in the absence of disorder and emphasize the role of two order parameters in the problem, viz. phase order and charge order. We focus on the two-dim ensional (2D) Bose Hubbard model in the limit of very large fillings, i.e., a 2D array of Josephson junctions. We find that the algebra of phase fluct uations is that of the Euclidean group E-2 in this limit, and show that the model is equivalent to two coupled XY models in (2 + 1) dimensions, one co rresponding to the phase degrees of freedom, and the other to the charge de grees of freedom. The Bose metal, then, is the phase in which both these de grees of freedom are disordered (as a result of quantum frustration). We an alyze the model in terms of its topological excitations and suggest that th ere is a strong indication that this state represents a surface of critical points, akin to the gapless spin liquid states. We find a remarkable consi stency of this scenario with certain low-T-c thin film experiments. [S0163- 1829(99)11525-X].