Microscopic nonequilibrium theory of double-barrier Josephson junctions

TL;DR

This paper develops a microscopic nonequilibrium theory for double-barrier Josephson junctions, explaining complex charge transport phenomena and the role of energy relaxation using the time-dependent quasiclassical Keldysh Green's function formalism.

Contribution

It introduces a detailed microscopic model incorporating time-dependent boundary conditions to analyze nonequilibrium charge transport in double-barrier Josephson junctions.

Findings

Quasiparticle current can show excess or deficit current.

Subgap conductance depends on junction parameters.

Energy relaxation influences intrinsic shunt behavior.

Abstract

We study nonequilibrium charge transport in a double-barrier Josephson junction, including nonstationary phenomena, using the time-dependent quasiclassical Keldysh Green's function formalism. We supplement the kinetic equations by appropriate time-dependent boundary conditions and solve the time-dependent problem in a number of regimes. From the solutions, current-voltage characteristics are derived. It is understood why the quasiparticle current can show excess current as well as deficit current and how the subgap conductance behaves as function of junction parameters. A time-dependent nonequilibrium contribution to the distribution function is found to cause a non-zero averaged supercurrent even in the presence of an applied voltage. Energy relaxation due to inelastic scattering in the interlayer has a prominent role in determining the transport properties of double-barrier junctions. Actual inelastic scattering parameters are derived from experiments. It is shown as an application of the microscopic model, how the nature of the intrinsic shunt in double-barrier junctions can be explained in terms of energy relaxation and the opening of Andreev channels.