Odd-triplet superconductivity in single-level quantum dots

TL;DR

This paper investigates how spin symmetry breaking in a single-level quantum dot coupled to a superconductor leads to the emergence of odd-triplet superconducting correlations, affecting electronic transport properties.

Contribution

It demonstrates the generation of odd-triplet correlations in single-level quantum dots through spin symmetry reduction, analyzed via a diagrammatic real-time technique.

Findings

Odd-triplet correlations are generated when spin symmetry is broken.

Superconducting correlations influence current and shot noise.

Full spin symmetry retains only even-singlet correlations.

Abstract

We study the interplay of spin and charge coherence in a single-level quantum dot. A tunnel coupling to a superconducting lead induces superconducting correlations in the dot. With full spin symmetry retained, only even-singlet superconducting correlations are generated. An applied magnetic field or attached ferromagnetic leads partially or fully reduce the spin symmetry, and odd-triplet superconducting correlations are generated as well. For single-level quantum dots, no other superconducting correlations are possible. We analyze, with the help of a diagrammatic real-time technique, the interplay of spin symmetry and superconductivity and its signatures in electronic transport, in particular current and shot noise.