Effect of zero-point fluctuations on the long-range phase coherence of granular films

The quantum Hamiltonian H=HC+HJ, with HJ the Josephson and HC the charging energy between grains, is studied. Renormalization-group equations are derived within a semiclassical approximation that show that there is a reentrant normal phase for nonzero HC; phase coherence is stable in a region of temperature that shrinks to zero as the quantum fluctuations grow, up to a critical value. The possible connection of these results to recent experiments is discussed.