Spin transport in high-mobility graphene on WS$_2$ substrate with electric-field tunable proximity spin-orbit interaction

TL;DR

This study demonstrates electric-field tunable spin transport in high-mobility graphene on WS$_2$, revealing strong proximity-induced spin-orbit coupling effects and the ability to modulate spin relaxation times via gating.

Contribution

First non-local spin transport measurements in graphene supported on WS$_2$, showing electric-field control of spin-orbit coupling and spin relaxation.

Findings

Spin signals are independent of WS$_2$ conduction state.

Spin-relaxation time is reduced to 10 ps in graphene-on-WS$_2$.

Electric field modulates spin relaxation time by a factor of four.

Abstract

Graphene supported on a transition metal dichalcogenide substrate offers a novel platform to study the spin transport in graphene in presence of a substrate induced spin-orbit coupling, while preserving its intrinsic charge transport properties. We report the first non-local spin transport measurements in graphene completely supported on a 3.5 nm thick tungsten disulfide (WS$_2$) substrate, and encapsulated from the top with a 8 nm thick hexagonal boron nitride layer. For graphene, having mobility up to 16,000 cm$^2$V$^{-1}$s$^{-1}$, we measure almost constant spin-signals both in electron and hole-doped regimes, independent of the conducting state of the underlying WS$_2$ substrate, which rules out the role of spin-absorption by WS$_2$. The spin-relaxation time $\tau_{\text{s}}$ for the electrons in graphene-on-WS$_2$ is drastically reduced down to~10 ps than $\tau_{\text{s}}$ ~ 800 ps in graphene-on-SiO$_2$ on the same chip. The strong suppression of $\tau_{\text{s}}$ along with a detectable weak anti-localization signature in the quantum magneto-resistance measurements is a clear effect of the WS$_2$ induced spin-orbit coupling (SOC) in graphene. Via the top-gate voltage application in the encapsulated region, we modulate the electric field by 1 V/nm, changing $\tau_{\text{s}}$ almost by a factor of four which suggests the electric-field control of the in-plane Rashba SOC. Further, via carrier-density dependence of $\tau_{\text{s}}$ we also identify the fingerprints of the D'yakonov-Perel' type mechanism in the hole-doped regime at the graphene-WS$_2$ interface.