Study on superconductor-insulator transitions in two-dimensional array of small Josephson junctions

We have studied the superconductor-insulator transitions in the two-dimensional regular arrays of Al/AlOx/Al small Josephson junctions. We studied the critical tunneling resistance and the temperature dependence of the resistance in detail by varying the interactions of the elementary excitation, i.e., charge solitons and vortices. The charging energy, junction resistance and the system width are the parameters to be changed. The results were compared with the theory of Fazio and Schon. Most of the observed results can be explained by the theory although we found some disagreements.