Quantum phase transitions in capacitively coupled two-dimensional Josephson-junction arrays

Quantum phase transitions in two layers of ultrasmall Josephson junctions, coupled capacitively with each other, are investigated. As the inter-layer capacitance is increased, the system at zero temperature is found to exhibit an insulator-to-superconductor transition. It is shown that, unlike in the case for one-dimensional arrays with a similar coupling configuration, the transition cannot be accounted for exclusively by particle-hole pairs.