Multiple Andreev reflections in a quantum dot coupled to superconductors: Effects of spin-orbit coupling

TL;DR

This paper investigates how spin-orbit coupling influences multiple Andreev reflections in a quantum dot with superconducting contacts, revealing dependence on dot shape, spin-orbit angle, and magnetic field orientation.

Contribution

It provides a detailed analysis of the effects of Rashba and Dresselhaus spin-orbit interactions on MAR features in a multilevel quantum dot, including how anisotropy and magnetic fields modulate these effects.

Findings

MAR peaks are modified by spin-orbit coupling but not suppressed.

Equal Rashba and Dresselhaus strengths enhance MAR peaks in isotropic dots.

Magnetic field angle affects conductance oscillations, revealing spin-orbit angle.

Abstract

We study the out-of-equilibrium current through a multilevel quantum dot contacted to two superconducting leads and in the presence of Rashba and Dresselhaus spin-orbit couplings, in the regime of strong dot-lead coupling. The multiple Andreev reflection (MAR) subgap peaks in the current voltage characteristics are found to be modified (but not suppressed) by the spin-orbit interaction, in a way that strongly depends on the shape of the dot confining potential. In a perfectly isotropic dot the MAR peaks are enhanced when the strength $\alpha_R$ and $\alpha_D$ of Rashba and Dresselhaus terms are equal. When the anisotropy of the dot confining potential increases the dependence of the subgap structure on the spin-orbit angle $\theta=\arctan(\alpha_D/\alpha_R)$ decreases. Furthermore, when an in-plane magnetic field is applied to a strongly anisotropic dot, the peaks of the non-linear conductance oscillate as a function of the magnetic field angle, and the location of the maxima and minima allows for a straightforward read-out of the spin-orbit angle $\theta$.