Superconducting transitions in ultrathin, amorphous, metallic multilayers

Multilayers of ultrathin superconducting a-Mo₇₉{Ge}₂₁$ and normal Ge-rich a-${Mo}_{1{{-}}x}Geₓ were prepared to study the effects of disorder on superconductivity in reduced dimensions. The superconducting transition temperatures of the multilayers as a function of composition and thickness of the normal metal show a systematic enhancement over the single film Tc. This effect can be attributed to a crossover from 2D single-film behavior to 3D bulk behavior as electron diffusion between individual superconducting layers increases. The nature of this crossover sheds light on the microscopic mechanisms reducing Tc.