PHASE-TRANSITIONS IN DOUBLE-LAYERED JOSEPHSON-JUNCTION ARRAYS

A system of two parallel Josephson junction arrays coupled by interlay er capacitances is considered in the situation where one layer is in t he vortex-dominated and the other in the charge-dominated regime. This system shows a symmetry (duality) of the relevant degrees of freedom, i.e. the vortices in one layer and the charges in the other. The char ges feel the magnetic field created by vortices, and, vice versa, the vortices feel a gauge field created by charges. For long-range interac tion of the charges the system exhibits two Berezinskii-Kosterlitz-Tho uless transitions, one for vortices and another one for charges. suppr esses the temperature of vortex-unbinding transition. It further repla ces the charge-unbinding transition by a crossover, which is smeared a lready for weak interlayer coupling.