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.
Categories: cond-mat.dis-nn cond-mat.mes-hall