Out-of-plane spin-to-charge conversion at low temperatures in graphene/MoTe$_2$ heterostructures

TL;DR

This study demonstrates omni-directional spin-to-charge conversion at low temperatures in graphene/MoTe$_2$ heterostructures, including an unconventional out-of-plane component likely due to the spin Hall effect in proximitized graphene.

Contribution

It reveals low-temperature out-of-plane spin-to-charge conversion in graphene/MoTe$_2$ heterostructures, expanding understanding of spin-charge interconversion in low-symmetry 2D materials.

Findings

Charge conversion for out-of-plane spins emerges below 100 K.

Unconventional spin-to-charge conversion is symmetry-allowed in the heterostructure.

Omni-directional spin-to-charge conversion observed at low temperatures.

Abstract

Multi-directional spin-to-charge conversion - in which spin polarizations with different orientations can be converted into a charge current in the same direction - has been demonstrated in low-symmetry materials and interfaces. This is possible because, in these systems, spin to charge conversion can occur in unconventional configurations in which spin polarization and charge current where charge current, spin current and polarization do not need to be mutually orthogonal. Here, we explore, in the low temperature regime, the spin-to-charge conversion in heterostructures of graphene with the low-symmetry 1T' phase of MoTe$_2$. First, we observe the emergence of charge conversion for out-of-plane spins at temperatures below 100 K. This unconventional component is allowed by the symmetries of both MoTe$_2$ and graphene and likely arises from spin Hall effect in the spin-orbit proximitized graphene. Moreover, we examine the low-temperature evolution of non-local voltage signals arising from the charge conversion of the two in-plane spin polarizations, which have been previously observed at higher temperature. As a result, we report omni-directional spin-to-charge conversion - for all spin polarization orientations - in graphene/MoTe${_2}$ heterostructures at low temperatures.