Charge glass in two-dimensional arrays of capacitively coupled grains with random offset charges

We study the effect of random offset charges in the insulator to conductor transition in systems of capacitively coupled grains, as realized in two-dimensional arrays of ultrasmall Josephson junctions. In presence of disorder, the conductive transition and charge ordering at nonzero gate voltages are both destroyed for any degree of disorder $\sigma$ at finite temperatures $T$, in the thermodynamic limit, but crossover effects will dominate at length scales smaller than $\xi_{\sigma, T}=T^{-\nu} f(\sigma T^{-\nu})$, where $\nu$ is the thermal critical exponent of the zero-temperature charge glass transition. The conductance is linear and thermally activated but nonlinear behavior sets in at a crossover voltage which decreases as temperature decreases. For large disorder, the results are supported by Monte Carlo dynamics simulations of a Coulomb gas with offset charges and are consistent with the thermally activated behavior found in recent experiments.