Andreev current enhancement and subgap conductance of superconducting hybrid structures in the presence of a small spin-splitting field

TL;DR

This paper studies how small spin-splitting fields can enhance Andreev current and affect subgap conductance in superconducting hybrid structures, revealing new effects and measurement techniques.

Contribution

It demonstrates the enhancement of Andreev current by spin-splitting fields above a critical bias voltage and proposes conductance measurement as a method to determine spin-splitting strength.

Findings

Andreev current is enhanced above a critical bias voltage V* by spin-splitting fields.

Finite temperature causes a peak in Andreev current near the superconducting gap.

Differential conductance can accurately measure small spin-splitting fields.

Abstract

We investigate the subgap transport properties of a S-F-Ne structure. Here S (Ne) is a superconducting (normal) electrode, and F is either a ferromagnet or a normal wire in the presence of an exchange or a spin- splitting Zeeman field respectively. By solving the quasiclassical equations we first analyze the behavior of the subgap current, known as the Andreev current, as a function of the field strength for different values of the voltage, temperature and length of the junction. We show that there is a critical value of the bias voltage V * above which the Andreev current is enhanced by the spin-splitting field. This unexpected behavior can be explained as the competition between two-particle tunneling processes and decoherence mechanisms originated from the temperature, voltage and exchange field respectively. We also show that at finite temperature the Andreev current has a peak for values of the exchange field close to the superconducting gap. Finally, we compute the differential conductance and show that its measurement can be used as an accurate way of determining the strength of spin-splitting fields smaller than the superconducting gap.