Determining spin-orbit coupling in graphene by quasiparticle interference imaging

TL;DR

This study demonstrates a method to quantitatively determine spin-orbit coupling in graphene on WSe2 by analyzing quasiparticle interference patterns, revealing larger-than-expected SOC values consistent with transport experiments.

Contribution

The paper introduces a novel approach using quasiparticle interference imaging to measure the magnitude and nature of induced spin-orbit coupling in graphene heterostructures.

Findings

Induced SOC includes valley-Zeeman and Rashba components with specific magnitudes.

Backscattering presence correlates with SOC strength and can be used for measurement.

Results align with previous transport measurements, validating the method.

Abstract

Inducing and controlling spin-orbit coupling (SOC) in graphene is key to create topological states of matter, and for the realization of spintronic devices. Placing graphene onto a transition metal dichalcogenide is currently the most successful strategy to achieve this goal, but there is no consensus as to the nature and the magnitude of the induced SOC. Here, we show that the presence of backscattering in graphene-on-WSe$_2$ heterostructures can be used to probe SOC and to determine its strength quantitatively, by imaging quasiparticle interference with a scanning tunneling microscope. A detailed theoretical analysis of the Fourier transform of quasiparticle interference images reveals that the induced SOC consists of a valley-Zeeman ($\lambda_{\text{vZ}}\approx 2$ meV) and a Rashba ($\lambda_\text{R}\approx 15$ meV) term, one order of magnitude larger than what theory predicts, but in excellent agreement with earlier transport experiments. The validity of our analysis is confirmed by measurements on a 30 degree twist angle heterostructure that exhibits no backscattering, as expected from symmetry considerations. Our results demonstrate a viable strategy to determine SOC quantitatively by imaging quasiparticle interference.