Phase diagram of Josephson junction arrays with capacitive disorder

We study the phase diagram at finite temperature of Josephson junction arrays with capacitive disorder (i.e., random offset charges and/or random charging energies): in the limit of large particle numbers per junction, this is a remarkable physical realization of the disordered boson Hubbard model. By using a mean-field approximation, we compute the average free energy and the equation for the phase boundary line between the insulating and the superconducting phase. We find that the Mott-insulating lobe structure disappears for large variance ($\sigma \gtrsim e$) of the offset charges probability distribution. Further, with nearest-neighbor interactions, the insulating lobe around $q=e$ is destroyed even for small values of $\sigma$. In the case of random charging energies, until the variance of the distribution reaches some critical value the superconducting phase increases in comparison to the situation in which all self-capacitances are equal.