Superconductor-insulator transition in a two-dimensional array of resistively shunted small josephson junctions

We have fabricated two-dimensional (2D) small-Josephson-junction arrays of which each Al-AlOx-Al junction is shunted by a Cr resistor. The arrays with large junction resistance and large charging energy show a transition from insulating to superconducting behavior when the shunt resistance is lowered below a critical value, which is close to 2R(Q) ( R(Q) identical withh/4e(2) = 6.45 kOmega). The measured phase diagram is consistent with theories of quantum-fluctuation-driven and dissipation-driven phase transitions in the 2D Josephson-junction array with Ohmic shunt resistors.