Berry curvature-induced local spin polarisation in gated graphene/WTe$_2$ heterostructures

TL;DR

This study demonstrates local, gate-tunable spin polarization in graphene/WTe2 heterostructures driven by Berry curvature effects, revealing out-of-plane spin accumulation despite in-plane charge transport, advancing nanoscale spin control.

Contribution

It introduces a magneto-optical Kerr microscopy approach to spatially resolve local spin polarization in 2D heterostructures and develops a theoretical model linking spin signals to Berry curvature and symmetry.

Findings

Out-of-plane spin accumulation observed with in-plane current.

Gate- and bias-dependent Kerr signal explained by interlayer tunneling.

Potential for topological spintronics applications.

Abstract

Full experimental control of local spin-charge interconversion is of primary interest for spintronics. Heterostructures combining graphene with a strongly spin-orbit coupled two-dimensional (2D) material enable such functionality by design. Electric spin valve experiments have provided so far global information on such devices, while leaving the local interplay between symmetry breaking, charge flow across the heterointerface and aspects of topology unexplored. Here, we utilize magneto-optical Kerr microscopy to resolve the gate-tunable, local current-induced spin polarisation in graphene/WTe$_2$ van der Waals (vdW) heterostructures. It turns out that even for a nominal in-plane transport, substantial out-of-plane spin accumulation is induced by a corresponding out-of-plane current flow. We develop a theoretical model which explains the gate- and bias-dependent onset and spatial distribution of the massive Kerr signal on the basis of interlayer tunnelling, along with the reduced point group symmetry and inherent Berry curvature of the heterostructure. Our findings unravel the potential of 2D heterostructure engineering for harnessing topological phenomena for spintronics, and constitute an important further step toward electrical spin control on the nanoscale.