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 lowere d below a critical value, which is close to 2R(Q) (R-Q equivalent to h/4e(2 ) = 6.45 k Omega). The measured phase diagram is consistent with theories o f quantum-fluctuation-driven and dissipation-driven phase transitions in th e 2D Josephson-junction array with Ohmic shunt resistors.