Intrinsic spin-orbit interaction in diffusive normal wire Josephson weak links: supercurrent and density of states

TL;DR

This paper investigates how intrinsic spin-orbit interactions influence supercurrent and density of states in superconductor-nanowire-superconductor junctions, revealing long-range triplet supercurrents and 0-$ extpi$ transitions.

Contribution

It demonstrates the emergence of long-range spin triplet supercurrents due to intrinsic spin-orbit coupling in diffusive SNS junctions with spin-splitting fields, using numerical and analytical solutions of Usadel equations.

Findings

Spin-orbit interaction induces long-range triplet supercurrents.

Rotation of the exchange field causes 0-$ extpi$ state transitions.

Zero-energy peak appears in the density of states.

Abstract

We study the effect of the intrinsic (Rashba or Dresselhaus) spin-orbit interaction in superconductor--nanowire--superconductor (SNS) weak links in the presence of a spin-splitting field that can result either from an intrinsic exchange field or the Zeeman effect of an applied field. We solve the full non-linear Usadel equations numerically and analyze the resulting supercurrent through the weak link and the behavior of the density of states in the center of the wire. We point out how the presence of the spin-orbit interaction gives rise to a long-range spin triplet supercurrent, which remains finite even in the limit of very large exchange fields. In particular, we show how rotating the field leads to a sequence of transitions between the 0 and $\pi$ states as a function of the angle between the exchange field and the spin-orbit field. Simultaneously, the triplet pairing leads to a zero-energy peak in the density of states. We proceed by solving the linearized Usadel equations, showing the correspondence to the solutions of the full equations and detail the emergence of the long-range supercurrent components. Our studies are relevant for on-going investigations of supercurrent in semiconductor nanowires in the limit of several channels and in the presence of disorder.