Evidence for a New Ordered Phase in a Periodic Array of Ultrasmall Josephson Junctions

The equilibrium properties of a periodic array of Josephson junctions are analyzed using a quantum Monte Carlo method. The model studied includes the effects of Josephson and charging energies in the presence of a constant, external transverse magnetic field. Results for the fully frustrated case are presented which imply the existence of a new coherent state with lower but finite superfluid density, separated from a higher-temperature coherent state by a strong first-order transition. Possible conditions under which our predictions can be tested experimentally are described.