Dynamics of Josephson junctions beyond the tunneling limit

TL;DR

This paper extends the RCSJ model for Josephson junctions beyond the tunneling limit, incorporating nonlinear dissipation and arbitrary current-phase relations, to better understand phenomena like the Josephson diode effect.

Contribution

It derives a generalized RCSJ model that includes nonlinear dissipative currents and arbitrary supercurrent relations, expanding the theoretical framework for Josephson junctions.

Findings

Derived a generalized fluctuation-dissipation theorem for nonlinear currents

Extended the RCSJ model to include non-tunneling regimes

Provided insights into the Josephson diode effect beyond traditional models

Abstract

The dynamics of the superconducting phase difference across a Josephson junction can be described within the resistively and capacitively shunted Josephson junction (RCSJ) model. Microscopic derivations of this model traditionally rely on the tunneling limit. Here, we present a derivation of a generalized version of the RCSJ model, which accounts for dissipative currents with nonlinear current-voltage characteristics as well as supercurrents with arbitrary current-phase relations. This requires a generalized fluctuation-dissipation theorem to describe the Langevin current, which we deduce along the lines of fluctuation theorems for mesoscopic conductors. Our work is motivated in particular by recent theories of the Josephson diode effect, which is not captured within the RCSJ model in the tunneling limit.