Probing the exchange field of a quantum-dot spin valve by a superconducting lead

TL;DR

This paper demonstrates that attaching a superconducting lead to a quantum-dot spin valve allows sensitive probing of the exchange field induced by ferromagnetic leads, revealing clear signatures in the supercurrent.

Contribution

It introduces a method to detect the exchange field in a quantum-dot spin valve using a superconducting lead, highlighting its sensitivity and observable effects.

Findings

Supercurrent shows signatures of the exchange field.

Signatures are detectable even at small ferromagnetic polarization.

The method provides a new way to probe exchange interactions in quantum dots.

Abstract

Electrons in a quantum-dot spin valve, consisting of a single-level quantum dot coupled to two ferromagnetic leads with magnetizations pointing in arbitrary directions, experience an exchange field that is induced on the dot by the interplay of Coulomb interaction and quantum fluctuations. We show that a third, superconducting lead with large superconducting gap attached to the dot probes this exchange field very sensitively. In particular, we find striking signatures of the exchange field in the symmetric component of the supercurrent with respect to the bias voltage applied between the ferromagnets already for small values of the ferromagnets' spin polarization.