Inverse Proximity Effect in a Strongly Correlated Electron System

An anomalous superconducting proximity effect between a strongly correlated electron system and a normal metal is demonstrated. The model system is a 2D ultrathin superconducting quench-condensed Pb film. Such a highly disordered film has a reduced transition temperature (T(c) = 1.7 K) due to the strong e(-)-e(-) interaction. Instead of weakening the superconductivity, an overlayer of Ag on Pb induces an increase of both the T(c) and the gap. The restoration of the electron screening brought about by the quasiparticles from the normal metal can explain this striking inverse proximity effect.