Quantum spin Hall states in graphene interacting with WS2 or WSe2

Kaloni, Thaneshwor P.; Kou, Liangzhi; Frauenheim, Thomas; Schwingenschlögl, Udo

doi:10.1063/1.4903895

Cited by 72 publications

(51 citation statements)

References 29 publications

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“…One promising objective is to increase the spin-orbit coupling (SOC) in graphene as this may offer numerous possibilities, including the generation of a pure spin current through the spin-Hall effect or the manipulation of spin currents through an electric field. Bringing graphene into the proximity of transition metal dichalcogenides (TMDCs) has been predicted theoretically [6,7] and observed experimentally [8][9][10][11] to increase SOC in graphene. Furthermore, transport measurements [12] and recent Raman measurements indicate the suitability of these substrates for high mobility graphene [13].…”

Section: Introductionmentioning

confidence: 99%

Magnetotransport in heterostructures of transition metal dichalcogenides and graphene

et al. 2017

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We use a van der Waals pickup technique to fabricate different heterostructures containing WSe 2 (WS 2 ) and graphene. The heterostructures were structured by plasma etching, contacted by one-dimensional edge contacts, and a top gate was deposited. For graphene/WSe 2 /SiO 2 samples we observe mobilities of ∼12 000 cm 2 V −1 s −1 . Magnetic-field-dependent resistance measurements on these samples show a peak in the conductivity at low magnetic fields. This dip is attributed to the weak antilocalization (WAL) effect, stemming from spin-orbit coupling. Samples where graphene is encapsulated between WSe 2 (WS 2 ) and hexagonal boron nitride show a much higher mobility of up to ∼120 000 cm 2 V −1 s −1 . However, in these samples no WAL peak can be observed. We attribute this to a transition from the diffusive to the quasiballistic regime. At low magnetic fields a resistance peak appears, which we ascribe to a size effect due to boundary scattering. Shubnikov-de Haas oscillations in fully encapsulated samples show all integer filling factors due to complete lifting of the spin and valley degeneracies.

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Section: Introductionmentioning

confidence: 99%

Magnetotransport in heterostructures of transition metal dichalcogenides and graphene

et al. 2017

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“…In fact, SOC can be significantly enhanced either by chemical functionalization-coating of graphene with light [33][34][35][36][37][38][39] or heavy [40][41][42][43] adatoms accompanied by band gap openingor by a variety of proximity effects resulting from substrates or due to scaffolding of different 2d materials 44 . Tangible examples are CVD graphene grown on Cu and Ni substrates [45][46][47] , or graphene placed on top of transition metal dichalcogenides [48][49][50][51] .…”

Section: Introductionmentioning

confidence: 99%

Model spin-orbit coupling Hamiltonians for graphene systems

2017

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We present a detailed theoretical study of effective spin-orbit coupling (SOC) Hamiltonians for graphene based systems, covering global effects such as proximity to substrates and local SOC effects resulting, for example, from dilute adsorbate functionalization. Our approach combines group theory and tight-binding descriptions. We consider structures with global point group symmetries D 6h , D 3d , D 3h , C6v, and C3v that represent, for example, pristine graphene, graphene mini-ripple, planar boron-nitride, graphene on a substrate and free standing graphone, respectively. The presence of certain spin-orbit coupling parameters is correlated with the absence of the specific point group symmetries. Especially in the case of C6v-graphene on a substrate, or transverse electric field-we point out the presence of a third SOC parameter, besides the conventional intrinsic and Rashba contributions, thus far neglected in literature. For all global structures we provide effective SOC Hamiltonians both in the local atomic and Bloch forms. Dilute adsorbate coverage results in the local point group symmetries C6v, C3v, and C2v which represent the stable adsorption at hollow, top and bridge positions, respectively. For each configuration we provide effective SOC Hamiltonians in the atomic orbital basis that respect local symmetries. In addition to giving specific analytic expressions for model SOC Hamiltonians, we also present general (no-go) arguments about the absence of certain SOC terms.

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“…In the field of spintronics, graphene has exceptional charge transport properties but weak spin-orbit coupling (SOC) on the order of 10 µeV [8], which makes it ideal for long-distance spin transport [9][10][11] but ineffective for generating or manipulating spin currents. 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].…”

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confidence: 99%

Giant Spin Lifetime Anisotropy in Graphene Induced by Proximity Effects

et al. 2017

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We report on fundamental aspects of spin dynamics in heterostructures of graphene and transition metal dichalcogenides (TMDCs). By using realistic models derived from first principles we compute the spin lifetime anisotropy, defined as the ratio of lifetimes for spins pointing out of the graphene plane to those pointing in the plane. We find that the anisotropy can reach values of tens to hundreds, which is unprecedented for typical 2D systems with spin-orbit coupling and indicates a qualitatively new regime of spin relaxation. This behavior is mediated by spin-valley locking, which is strongly imprinted onto graphene by TMDCs. Our results indicate that this giant spin lifetime anisotropy can serve as an experimental signature of materials with strong spin-valley locking, including graphene/TMDC heterostructures and TMDCs themselves. Additionally, materials with giant spin lifetime anisotropy can provide an exciting platform for manipulating the valley and spin degrees of freedom, and for designing novel spintronic devices. [3,4], where the combined system might be engineered for specific applications [5] or might enable the exploration of new phenomena [6,7]. In the field of spintronics, graphene has exceptional charge transport properties but weak spin-orbit coupling (SOC) on the order of 10 µeV [8], which makes it ideal for long-distance spin transport [9-11] but ineffective for generating or manipulating spin currents. 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]. Fits to the magnetoconductance yielded spin lifetimes τ s ≈ 5 ps, which is two to three orders of magnitude lower than graphene on traditional substrates [10,31]. It was later asserted that after the removal of a temperatureindependent background, τ s becomes at most only a few hundred femtoseconds [26]. Nonlocal Hanle measurements, meanwhile, have revealed spin lifetimes up to a few tens of picoseconds [27][28][29] that can be tuned by a back gate [28,29]. Finally, charge transport measure-

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Quantum spin Hall states in graphene interacting with WS2 or WSe2

Cited by 72 publications

References 29 publications

Magnetotransport in heterostructures of transition metal dichalcogenides and graphene

Magnetotransport in heterostructures of transition metal dichalcogenides and graphene

Model spin-orbit coupling Hamiltonians for graphene systems

Giant Spin Lifetime Anisotropy in Graphene Induced by Proximity Effects

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