Multiple Andreev reflections in diffusive SINIS and SIFIS junctions

TL;DR

This paper analyzes multiple Andreev reflections in diffusive SINIS and SIFIS junctions, revealing how thermalization and exchange fields influence the current-voltage characteristics and subharmonic gap structures.

Contribution

It provides an analytical model for noncoherent multiple Andreev reflections in diffusive junctions with low-transparency interfaces, including effects of ferromagnetism.

Findings

Current dominated by noncoherent MAR at intermediate temperatures

Exchange field causes splitting of subharmonic gap structure

Thermalization effects are crucial for observed phenomena

Abstract

We study Multiple Andreev Reflections in long diffusive superconductor(S)-normal metal(N)-superconductor junctions with low-transparency interfaces. Assuming strong thermalization in the weak link we calculate the current-voltage dependence $I(V)$. At intermediate temperatures, $E_\mathrm{Th}\ll T\ll\Delta$, the current is dominated by noncoherent multiple Andreev reflections and is obtained analytically. The results are generalized to a ferromagnetic junction. We find that the exchange field produces a non-trivial splitting of the subharmonic gap structure. This effect relies on thermalization and vanishes in SFS junctions with no energy relaxation in the weak link.