Creation of equal-spin triplet superconductivity at the Al/EuS interface

S Diesch,P Machon,C Sürgers,M Wolz,D Beckmann,E Scheer,W Belzig

doi:10.1038/s41467-018-07597-w

S Diesch, P Machon + Show 5 more

Open Access

https://doi.org/10.1038/s41467-018-07597-w

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Abstract

In conventional superconductors, electrons of opposite spins are bound into Cooper pairs. However, when the superconductor is in contact with a non-uniformly ordered ferromagnet, an exotic type of superconductivity can appear at the interface, with electrons bound into three possible spin-triplet states. Triplet pairs with equal spin play a vital role in low-dissipation spintronics. Despite the observation of supercurrents through ferromagnets, spectroscopic evidence for the existence of equal-spin triplet pairs is still missing. Here we show a theoretical model that reveals a characteristic gap structure in the quasiparticle density of states which provides a unique signature for the presence of equal-spin triplet pairs. By scanning tunnelling spectroscopy we measure the local density of states to reveal the spin configuration of triplet pairs. We demonstrate that the Al/EuS interface causes strong and tunable spin-mixing by virtue of its spin-dependent transmission.

Highlights

In conventional superconductors, electrons of opposite spins are bound into Cooper pairs
In that work a Nb/Ho bilayer has been probed from the superconducting side and the obtained spectra were compared to a specialised theoretical model relying on the chiral magnetic state of Ho and pinning effects occurring at the Nb/Ho interface
The influence of the spin-dependent phase shifts are expected to be much weaker on the S side of the interface, resulting in only small amplitudes of the subgap features. To address these two issues, we study here the local density of states (LDOS) of an S/FI/N trilayer, where FI is a ferromagnetic insulator with non-collinear magnetisation

Summary

Introduction

Electrons of opposite spins are bound into Cooper pairs. D e studies, the appearance of spectra with triplet gap features corresponds to areas with at least two magnetisation directions which are non-collinear.

Results

Conclusion