Superconductivity enhancement in screened ultrathin metal films

We have studied superconductivity in thin quench-condensed bismuth films deposited on a 3 nm oxide layer covering a thick aluminium film, it was found that these Ri films have superconducting transition temperatures significantly larger than those of similar films deposited directly on glass. The enhancement of superconductivity is attributed to partial screening of the Coulomb interaction between conduction electrons in the bismuth films. The proximity of the thick metal film, even without any electrical contact to the thin film, reduces the interaction quantum correction to conductivity, the effect responsible for suppression of superconductivity in high-resistance films. However, the enhancement is less than predicted by the Finkelstein theory. It was also found that screened films showed an increased resistivity, a result attributed to reduced electron-electron scattering in the weak-localization quantum correction to conductivity.