Microscopic Theory of Josephson Mesoscopic Constrictions

Abstract

We present a microscopic theory for the d.c. Josephson effect in model mesoscopic constrictions. Our method is based on a non-equilibrium Green function formalism which allows for a self-consistent determination of the order parameter profile along the constriction. The various regimes defined by the different length scales (Fermi wavelength $λ_F$, coherence length $ξ_0$ and constriction length $L_C$) can be analyzed, including the case where all these lengths are comparable. For the case $λ_F \tilde{<} (L_C,ξ_0)$ phase oscillations with spatial period $λ_F/2$ can be observed. In the case of $L_C>ξ_0$ solutions with a phase-slip center inside the constriction can be found, in agreement with previous phenomenological theories.