Charging Energy and Superconducting Reentrant Behavior of Zero Point Fluctuated Arrays of Josephson Junctions

摘要

High sheet resistance coplanar arrays with very high densities of small Josephson Junctions (JJs) have been measured. They present a reentrance of the critical current with an exponential behavior. This suggests a thermal activation in the number of Cooper pairs tunneling across the barrier, in which tunneling is reduced by charging energy, an effect partially compensated by the thermal bath. In addition, a sample of intermediate sheet resistance also presents a new regime at low temperatures, where the critical current raises again, but remains much below the expected unfluctuated critical current. Sample parameters indicate that, in this regime, the Josephson coupling energy might become larger than the otherwise dominating charging energy. 20 refs., 5 figs.