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 $(T_c=1.7\mathrm{}\mathrm{K})$ 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.