Theory of Subharmonic Gap Structure in Superconducting Mesoscopic Tunnel Contacts

Abstract

We develop a theory of subharmonic gap structure (SGS) in superconducting one-mode tunnel junction. The subgap current is attributed to inelastic multichannel quasiparticle tunneling assisted by the time-dependent phase difference at the contact. Opening of inelastic scattering channels is manifested in onsets and peaks of tunnel current forming SGS. An explicit analytical expansion is found for the tunnel current in powers of small contact transparency.