Quantum effects in a superconducting-glass model

Abstract

We study disordered Josephson-junction arrays with long-range interaction and charging effects. The model consists of two orthogonal sets of positionally disordered N parallel filaments (or wires) Josephson coupled at each crossing and in the presence of a homogeneous and transverse magnetic field. The large charging energy (resulting from small self-capacitance of the ultrathin wires) introduces important quantum fluctuations of the superconducting phase within each filament. Positional disorder and magnetic-field frustration induce spin-glass-like ground states, characterized by not having long-range order of the phases. The stability of this phase is destroyed for sufficiently large charging energy. We have evaluated the temperature vs charging energy phase diagram by extending the methods developed in the theory of infinite-range spin glasses, in the limit of large magnetic field. The phase diagram in the different temperature regimes is evaluated by using a variety of methods, to wit: semiclassical WKB and variational methods, Rayleigh-Schrödinger perturbation theory, and pseudospin effective Hamiltonians. Possible experimental consequences of these results are briefly discussed.

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