Current rectification in junctions with spin-split superconductors

TL;DR

This paper investigates current rectification in junctions with spin-split superconductors, revealing a voltage-symmetric component in the I-V curve that enables rectification, with potential applications in superconducting diodes and radiation detectors.

Contribution

It demonstrates the existence of current rectification due to electron-hole asymmetry in spin-polarized superconductor junctions, including analysis of heat currents and noise for detector applications.

Findings

Rectified current is proportional to junction spin polarization.

The I-V curve exhibits a voltage-symmetric component.

Rectification depends strongly on the bias frequency.

Abstract

Spin-split superconductors exhibit an electron-hole asymmetric spin-resolved density of states, but the symmetry is restored upon averaging over spin. On the other hand, asymmetry appears again in tunneling junctions of spin-split superconductors with a spin-polarized barrier. As demonstrated recently in both theory and experiment, this fact leads to a particularly strong thermoelectric effect in superconductor-ferromagnet structures. In this work we show another important effect stemming from the electron-hole asymmetry - current rectification. We calculate the charge current in spin-polarized tunnel junctions of normal metal and a spin-split superconductor with AC and DC voltage bias. In the DC case, the I-V curve is not fully antisymmetric and has a voltage-symmetric component due to spin polarization. This translates to the existence of a rectified current in the AC case, which is proportional to the spin polarization of the junction and strongly depends on the frequency of the applied bias. We discuss possible applications of the rectification effect, including a diode for superconducting electronics and radiation detectors. The analysis of the rectified charge current is supplemented by the discussion of heat current and relevant noise correlators, where electron-hole asymmetry also plays an important role, and which are useful for applications in detectors.