Positional disorder in Josephson-junction arrays: Experiments and simulations

Abstract

We present the results of measurements on proximity-effect arrays with deliberate positional disorder, characterized by a parameter ${\ensuremath{\Delta}}^{\mathrm{*}}$. This system provides an experimental realization of XY magnet with random Dzyaloshinskii-Moriya interactions. In measurements of resistance versus perpendicular magnetic field, R(${f}_{0}$), we find strong evidence for a critical field ${f}_{c}$\ensuremath{\propto}1/${\ensuremath{\Delta}}^{\mathrm{*}}$ beyond which phase coherence is destroyed. Our Monte Carlo simulations show evidence for reentrant behavior in the helicity modulus Y, but with Y always finite at the lowest temperatures. Such a critical field and reentrance were predicted by Granato and Kosterlitz.