Phase transition in positionally disordered Josephson-junction arrays in a transverse magnetic field

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Abstract
The critical behavior of positionally disordered two-dimensional Josephson-junction arrays in a transverse magnetic field is studied by Monte Carlo simulations. We consider a model in which each superconducting element is randomly displaced from its ideal position on a square lattice by a small amount. The effective strength of the disorder is changed by varying the magnitude of the transverse magnetic field. We consider those values of the magnetic field for which the parameter 〈f〉 that measures the average flux through an elementary plaquette in units of the flux quantum is integral. For 〈f〉=1 and 〈f〉=3, we find Kosterlitz-Thouless-type phase transition from a normal to a superconducting phase. For 〈f〉=5 and 〈f〉=7, the results suggest a spin-glass-like freezing over the time scales of the simulations. We do not find any evidence for a low-temperature reentrant transition for any value of 〈f〉.