Proximity effect in superconductor/conical magnet heterostructures

TL;DR

This paper investigates how conical magnetic interface layers influence the generation of equal-spin spin-triplet Cooper pairs in superconductor/holmium heterostructures, using microscopic calculations to analyze the effects of magnetic angles.

Contribution

It provides a detailed analysis of how conical magnetic angles affect triplet pairing correlations in superconductor/holmium heterostructures, advancing understanding of long-range proximity effects.

Findings

Equal-spin triplet pairing is enhanced by specific conical magnetic configurations.

The angles $eta$ and $eta$ significantly influence the pairing correlations.

Results are obtained through self-consistent Bogoliubov-de Gennes calculations.

Abstract

The presence of a spin-flip potential at the interface between a superconductor and a ferromagnetic metal allows for the generation of equal-spin spin-triplet Cooper pairs. These Cooper pairs are compatible with the exchange interaction within the ferromagnetic region and hence allow for the long-range proximity effect through a ferromagnet or half-metal. One suitable spin-flip potential is provided by incorporating the conical magnet Holmium (Ho) into the interface. The conical magnetic structure is characterised by an opening angle $\alpha$ with respect to the crystal $c$-axis and a turning (or pitch) angle $\beta$ measuring the rotation of magnetisation with respect to the adjacent layers. Here, we present results showing the influence of conical magnet interface layers with varying $\alpha$ and $\beta$ on the efficiency of the generation of equal-spin spin-triplet pairing. The results are obtained by self-consistent solutions of the microscopic Bogoliubov$-$de Gennes equations in the clean limit within a tight-binding model of the heterostructure. In particular, the dependence of unequal-spin and equal-spin spin-triplet pairing correlations on the conical magnetic angles $\alpha$ and $\beta$ are discussed in detail.