Spin transport in high-mobility graphene on WS2 substrate with electric-field tunable proximity spin-orbit interaction

Abstract

Graphene supported on a transition metal dichalcogenide substrate offers a novel platform to study the spin transport in graphene in the presence of a substrate-induced spin-orbit coupling while preserving its intrinsic charge transport properties. We report the first nonlocal spin transport measurements in graphene completely supported on a 3.5-nm-thick tungsten disulfide (${\mathrm{WS}}_{\text{2}}$) substrate, and encapsulated from the top with an 8-nm-thick hexagonal boron nitride layer. For graphene, having mobility up to 16 000 ${\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, we measure almost constant spin signals both in electron and hole-doped regimes, independent of the conducting state of the underlying ${\mathrm{WS}}_{2}$ substrate, which rules out the role of spin-absorption by ${\mathrm{WS}}_{2}$. The spin-relaxation time ${\ensuremath{\tau}}_{\text{s}}$ for the electrons in graphene-on-${\mathrm{WS}}_{2}$ is drastically reduced down to $\ensuremath{\sim}10$ ps from ${\ensuremath{\tau}}_{\text{s}}\ensuremath{\sim}800$ ps in graphene-on-${\mathrm{SiO}}_{2}$ on the same chip. The strong suppression of ${\ensuremath{\tau}}_{\text{s}}$ along with a detectable weak antilocalization signature in the quantum magnetoresistance measurements is a clear effect of the ${\mathrm{WS}}_{2}$-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 ${\ensuremath{\tau}}_{\text{s}}$ almost by a factor of four, which suggests electric-field control of the in-plane Rashba SOC. Further, via the carrier-density dependence of ${\ensuremath{\tau}}_{\text{s}}$, we also identify the fingerprints of the D'yakonov-Perel' type mechanism in the hole-doped regime at the graphene-${\mathrm{WS}}_{2}$ interface.