Partially resummed perturbation theory for multiple Andreev reflections in a short three-terminal Josephson junction

TL;DR

This paper introduces a computationally efficient semi-analytical method to model nonequilibrium transport in three-terminal Josephson junctions, accurately capturing multiple Andreev reflections and multipair resonances across the full voltage range.

Contribution

A novel partially resummed perturbation theory approach that simplifies calculations while maintaining compatibility with existing results for complex Josephson junctions.

Findings

Method accurately describes current across voltage range

Multipair critical current exceeds background MAR current at intermediate transparency

Results align with previous studies on multipair resonances

Abstract

In a transparent three-terminal Josephson junction, modeling nonequilibrium transport is numerically challenging, owing to the interplay between multiple Andreev reflection (MAR) thresholds and multipair resonances in the pair current. An approximate method, coined as "partially resummed perturbation theory in the number of nonlocal Green's functions", is presented that can be operational on a standard computer and demonstrates compatibility with results existing in the literature. In a linear structure made of two neighboring interfaces (with intermediate transparency) connected by a central superconductor, tunneling through each of the interfaces separately is taken into account to all orders. On the contrary, nonlocal processes connecting the two interfaces are accounted for at the lowest relevant order. This yields logarithmically divergent contributions at the gap edges, which are sufficient as a semi-quantitative description. The method is able to describe the current in the full two-dimensional voltage range, including commensurate as well as incommensurate values. The results found for the multipair (for instance quartet) current-phase characteristics as well as the MAR thresholds are compatible with previous results. At intermediate transparency, the multipair critical current is much larger than the background MAR current, which supports an experimental observation of the quartet and multipair resonances. The paper provides a proof of principle for addressing in the future the interplay between quasiparticles and multipairs in four-terminal structures.