Superconductor-insulator transition in thin metallic films induced by interface-roughness scattering

Disorder due to small random variations of the width $L$ of thin films leads to scattering for superconducting particles. It is shown for the first time that this disorder, interface-roughness scattering for bosons, gives rise to a superconductor-insulator transition, as observed for instance in amorphous Bi films. We present a model calculation of a disordered interacting Bose condensate in a quantum well of finite width $L$. Films with $L<L_C$ are insulating, with $L_C$ as the critical width, while films with $L>L_C$ are superconducting. Disorder strongly reduces the critical temperature $T_C$ of the superconducting phase and $T_C$ vanishes at $L_C$. A phenomenological two-fluid model is also discussed.