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Supersolid Phases in
Underdamped Josephson Arrays: Quantum Monte Carlo Simulations

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Eric Roddick and David Stroud,
Department of Physics,
The Ohio State University,
Columbus, OH, 43210

We carry out a quantum Monte Carlo study of
Josephson arrays at temperature $T=0$ in the presence of an
offset voltage between array and substrate.
With diagonal and nearest-neighbor
charge coupling, we find two types of insulating lobes with different
types of charge order, and two types of superconducting regions.
One of these is a supersolid with coexisting long range phase coherence
and checkerboard charge order. The supersolid phase
is found to be robust even at half-integer filling.
With next-nearest neighbor coupling, there are two types of supersolid
phase, one with checkerboard and one with striped charge order.
Our phase diagram agrees with mean-field theory and with quantum Monte
Carlo results of van Otterlo {\it et al} in comparable regions of parameter
space, but differs in detail from that of a Bose-Hubbard model with nearest
neighbor charging energies, probably because of
differences in commutation relations.
PACS numbers: 74.20M, 74.50, 74.76, 05.30.J