Conductance and current noise of a superconductor/ferromagnet quantum point contact

TL;DR

This paper investigates how spin-dependent phase shifts at a superconductor/ferromagnet quantum point contact influence conductance and noise, revealing that noise measurements can provide additional insights into device properties.

Contribution

It demonstrates the significant impact of spin-dependent interfacial phase shifts on conductance and noise in superconductor/ferromagnet QPCs, highlighting the usefulness of noise measurements for device analysis.

Findings

SDIPS induces sub-gap resonances in conductance and Fano factor for low transparency.

Resonances are smoothed at high transparency but remain sensitive to SDIPS.

Noise measurements can reveal SDIPS effects not evident in conductance.

Abstract

We study the conductance and current noise of a superconductor/ferromagnet (S/F) single channel Quantum Point Contact (QPC) as a function of the QPC bias voltage, using a scattering approach. We show that the Spin-Dependence of Interfacial Phase Shifts (SDIPS) acquired by electrons upon scattering by the QPC can strongly modify these signals. For a weakly transparent contact, the SDIPS induces sub-gap resonances in the conductance and differential Fano factor curves of the QPC. For high transparencies, these resonances are smoothed, but the shape of the signals remain extremely sensitive to the SDIPS. We show that noise measurements could help to gain more information on the device, e.g. in cases where the SDIPS modifies qualitatively the differential Fano factor of the QPC but not the conductance.