Strong electron-hole symmetric Rashba spin-orbit coupling in graphene/monolayer transition metal dichalcogenide heterostructures

TL;DR

This study demonstrates strong, electron-hole symmetric Rashba spin-orbit coupling in graphene when placed on monolayer TMDs, revealing significant proximity effects and a Dyakonov-Perel relaxation mechanism with potential spintronic applications.

Contribution

It provides experimental evidence of strong Rashba SOC in graphene/TMD heterostructures with nearly symmetric electron-hole behavior, using CVD-grown monolayer TMDs and magnetoconductance analysis.

Findings

Rashba SOC energy of ~1.5 meV in graphene/WSe2

Rashba SOC energy of ~0.9 meV in graphene/MoS2

Spin relaxation dominated by Dyakonov-Perel mechanism

Abstract

Despite its extremely weak intrinsic spin-orbit coupling (SOC), graphene has been shown to acquire considerable SOC by proximity coupling with exfoliated transition metal dichalcogenides (TMDs). Here we demonstrate strong induced Rashba SOC in graphene that is proximity coupled to a monolayer TMD film, MoS2 or WSe2, grown by chemical vapor deposition with drastically different Fermi level positions. Graphene/TMD heterostructures are fabricated with a pickup-transfer technique utilizing hexagonal boron nitride, which serves as a flat template to promote intimate contact and therefore a strong interfacial interaction between TMD and graphene as evidenced by quenching of the TMD photoluminescence. We observe strong induced graphene SOC that manifests itself in a pronounced weak anti-localization (WAL) effect in the graphene magnetoconductance. The spin relaxation rate extracted from the WAL analysis varies linearly with the momentum scattering time and is independent of the carrier type. This indicates a dominantly Dyakonov-Perel spin relaxation mechanism caused by the induced Rashba SOC. Our analysis yields a Rashba SOC energy of ~1.5 meV in graphene/WSe2 and ~0.9 meV in graphene/MoS2, respectively. The nearly electron-hole symmetric nature of the induced Rashba SOC provides a clue to possible underlying SOC mechanisms.