A spin triplet supercurrent through the half-metallic ferromagnet CrO2

TL;DR

This paper demonstrates a Josephson supercurrent through the ferromagnet CrO2, indicating the presence of spin triplet superconductivity, which can be controlled by magnetization direction, opening avenues for spintronic applications.

Contribution

It provides experimental evidence of spin triplet supercurrent in a strong ferromagnet, showing conversion from singlet to triplet pairs at the interface, differing from previous theoretical models.

Findings

Supercurrent observed through CrO2, a strong ferromagnet

Supercurrent can be switched by changing magnetization direction

Conversion from singlet to triplet pairs at the interface inferred

Abstract

In general, conventional superconductivity should not occur in a ferromagnet, though it has been seen in iron under pressure. Moreover, theory predicts that the current is always carried by pairs of electrons in a spin singlet state, so conventional superconductivity decays very rapidly when in contact with a ferromagnet, which normally prohibits the existence of singlet pairs. It has been predicted that this rapid spatial decay would not occur when spin triplet superconductivity could be induced in the ferromagnet. Here we report a Josephson supercurrent through the strong ferromagnet CrO2, from which we infer that it is a spin triplet supercurrent. Our experimental setup is different from those envisaged in the earlier predictions, but we conclude that the underlying physical explanation for our result is a conversion from spin singlet to spin triplets at the interface. The supercurrent can be switched with the direction of the magnetization, analogous to spin valve transistors, and therefore could enable magnetization-controlled Josephson junctions.