Tunable spin–orbit coupling and symmetry-protected edge states in graphene/WS ₂

Abstract

We demonstrate clear weak anti-localization (WAL) effect arising from induced Rashba spin-orbit coupling (SOC) in WS2-covered single-layer and bilayer graphene devices. Contrary to the uncovered region of a shared single-layer graphene flake, WAL in WS2-covered graphene occurs over a wide range of carrier densities on both electron and hole sides. At high carrier densities, we estimate the Rashba SOC relaxation rate to be ∼ 0.2ps −1 and show that it can be tuned by transverse electric fields. In addition to the Rashba SOC, we also predict the existence of a'valley-Zeeman' SOC from first-principles calculations. The interplay between these two SOC's can open a non-topological but interesting gap in graphene; in particular, zigzag boundaries host four sub-gap edge states protected by time-reversal and crystalline symmetries. The graphene/WS2 system provides a possible platform for these novel edge states.

Spin Hall Effect and Weak Antilocalization in Graphene/Transition Metal Dichalcogenide Heterostructures

“…[16][17][18] Another route is the deposition of graphene onto transition metal dichalcogenides (TMDCs), 19,20 where a considerable enhancement of SOC in graphene interfaced with WS 2 or WSe 2 has been unveiled by measuring weak antilocalization (WAL) effects. [21][22][23] Additionally, large spin Hall effect signals have been reported in graphene/WS 2 heterostructures, 24 suggesting that such interfaces could be suitable for the optimization of pure spin currents and the development of spin-torque technologies. 7 However, the observation of SHE in graphene/TMDC systems has been difficult to reproduce, opening some debate about how intrinsic mechanisms inducing Hall effects are actually related to non-local resistance signals.…”

Giant Spin Lifetime Anisotropy in Graphene Induced by Proximity Effects

“…Previous analyses have concluded that the spin relaxation is dominated by Rashba SOC [25,30], which is seemingly at odds with the presence of giant spin lifetime anisotropy. By reanalyzing the magnetoconductance measurements of Ref.…”

“…To advance towards spin manipulation, recent work has focused on heterostructures of graphene and magnetic insulators [12][13][14][15][16] or strong SOC materials such as transition metal dichalcogenides (TMDCs) and topological insulators [17][18][19]. The SOC induced in graphene by a TMDC could enable phenomena such as topological edge states [20] or the spin Hall effect [21][22][23].To this end, a variety of recent experiments have explored spin transport in graphene/TMDC heterostructures [21,[24][25][26][27][28][29]. Magnetotransport measurements revealed that graphene in contact with WS 2 exhibits a large weak antilocalization (WAL) peak, revealing a strong SOC induced by proximity effects [24][25][26]30].…”

Quantum Hall effect in graphene with interface-induced spin-orbit coupling

“…Experiments and first-principle calculations point out to values of the coupling constants in the range of 0.1 − 10 meV 21,22 . We express our results in terms of a gate voltage which controls the Fermi energy.…”

“…Graphene has been proximity-coupled with a magnetic thin layer of YIG for transport 17 and spin-pumping 18 measurements. SOC was also induced by proximity effect in graphene on top of different transition metal Dichalcogenites (TMDC) [19][20][21][22] and graphene decorated with Gold 23 . More recently, spins were optically injected in graphene/TMDC systems 24,25 , also indicating the presence of SOC in the graphene layer.…”