Interface engineering of superconductor/normal metal heterostructures: the critical role of interface on proximity and inverse effect*

We investigate the crucial role of interface on superconducting proximity and its inverse effect, using epitaxially grown vertical/lateral superconductor/normal metal (S/N) heterostructures. The two different S/N heterostructures have utterly different interface nature: one is transparent and the other opaque. Because of the electrically transparent interface of the vertical heterostructure, electrons fully coherence in the vertical S/N heterostructure. Local tunneling spectroscopy and global superfluid density measurement show the uniform superconducting gap (SCG) throughout whole vertical S/N heterostructure with no discontinuity. In contrast, lateral S/N heterostruture reveals the spatial dependent SCG with an abrupt discontinuity due to the diffuse interface. Moreover, we found that for the vertical heterostructure in Cooper limit, electron-phonon coupling strength weakens as the thickness ratio of Pb to Ag is lower than 2.