Atomicscale Investigation of Proximity Effect at a Molecular-Superconductor-Metal Boundary

Proximity effects of nanoscale molecular clusters, (BETS)$_{2}$-GaCl$_{4}$, on Ag(111)have been investigated by using low temperature tunneling spectroscopy and spectroscopic mapping. At a far distance from the superconductor-metal boundary, the dI/dV tunneling spectroscopic data show the surface state on-set of two-dimensional nearly free electrons on Ag(111) surface at -65 mV. Strikingly, the intensity of the surface state rapidly decreases when the dI/dV data are recorded closer to the boundary. At $\sim$ 2nm distance, the surface state is completely quenched. Moreover, the formation of pseudo-gap state is already observed far from the metal-superconductor boundary, which later transform into the superconducting gap. This work provides detailed electronic structure evolution across a metal-superconductor boundary at an atomic scale.