Enhancement of the Critical Temperature Induced by the Quantum Size Effect in Superconducting Nanofilms

The interplay between the quantum size effect and superconductivity in the metallic Al nanofilms has been studied with the use of the self-consistent numerical solutions of the Bogoliubov-de Gennes equations. We have shown that the critical temperature of the metallic nanofilm oscillates as a function of the nanofilm thickness. This phenomenon results from the quasi-particle energy quantization induced by the confinement of electrons in the direction perpendicular to the film. For the ultrathin nanofilms with thickness 1-2 nm we have found that the critical temperature increases up to value several times higher as compared to the one measured in the bulk.