Spin Hall Effect and Origins of Nonlocal Resistance in Adatom-Decorated Graphene

Tuan, Dinh Van; Marmolejo‐Tejada, Juan M.; Waintal, Xavier; Nikolić, Branislav K.; Valenzuela, Sergio O.; Roche, Stephan

doi:10.1103/physrevlett.117.176602

Cited by 72 publications

(86 citation statements)

References 76 publications

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“…28,[52][53][54][55][56][57][58][59][60][61][62][63][64] In this paper we present a detailed symmetry analysis focusing on effective SOC Hamiltonians in a way that is complementary to Refs. [40,56,65].…”

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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Section: Introductionmentioning

confidence: 99%

Model spin-orbit coupling Hamiltonians for graphene systems

2017

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“…Nonlocal signals detected in H-shape graphene structures decorated with metallic particles have been interpreted as due to large spin Hall effects, owing to SOC by proximity effects [33]. Theoretical analysis suggests that the proximity SOC should indeed enhance the spin Hall effect [34,35], but also that the signal in the H-shape structures can be affected by non spin-related contributions, which can lead to incorrect interpretations [35,36]. More recent experiments using a ferromagnetic source/detector [7,[10][11][12] in multilayer graphene/Pt spin devices demonstrated large spin signals at room temperature, showing the potential of graphene-based devices for spin to charge conversion [37].…”

Section: Introductionmentioning

confidence: 99%

Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures

et al. 2017

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IntroductionSpin Hall effects (SHE) are a family of relativistic phenomena in which electrical currents generate transverse spin currents and vice versa as a consequence of spin-orbit coupling (SOC) [1]. In non-magnetic materials, they provide a versatile tool for the generation and detection of spin currents without the insertion of ferromagnets (FMs). Early theoretical investigations showed that the SHE can be of extrinsic [2,3] or intrinsic [1,4] origin. Experimental observations have been carried out in semiconductor and metallic systems by means of optical [5,6], electrical [7] and magnetization dynamics [8] methods, triggering many fundamental studies and potential applications [9].The exploration of the SHE using nonlocal (NL) measurements [7,10] have been frequently performed in metals using Pt as the large SOC material [11,12]. In semiconductor systems, detection and modulation of the inverse SHE (ISHE) has been achieved in n-GaAs by means of spin precession in combination with external electric fields [13]. These studies have led to a better comprehension of the phenomena and more accurate determination and control of the spinto-charge conversion efficiency, which is quantified by the spin Hall angle (α SHE ). For instance, α SHE can be enhanced by using metallic alloys [14,15], or tuned by changing the electrical resistivity [16]. Moreover, recent experiments have demonstrated that spin currents generated by the SHE can be large enough to switch the magnetization of nanomagnets [17,18] and induce fast domain wall motion [19], highlighting the potential use of the SHE in conventional spintronic devices [18] and pointing the path towards future spintronics without FMs.Additionally, 2D materials have emerged as promising system for spintronics owing to their tuneable electronic properties. In particular, graphene is attractive for both propagating and manipulating spin information over long distances because of its long spin-diffusion length λ s [20][21][22] AbstractSpin Hall effects have surged as promising phenomena for spin logics operations without ferromagnets. However, the magnitude of the detected electric signals at room temperature in metallic systems has been so far underwhelming. Here, we demonstrate a two-order of magnitude enhancement of the signal in monolayer graphene/Pt devices when compared to their fully metallic counterparts. The enhancement stems in part from efficient spin injection and the large spin resistance of graphene but we also observe 100% spin absorption in Pt and find an unusually large effective spin Hall angle of up to 0.15. The large spin-to-charge conversion allows us to characterise spin precession in graphene under the presence of a magnetic field. Furthermore, by developing an analytical model based on the 1D diffusive spin-transport, we demonstrate that the effective spinrelaxation time in graphene can be accurately determined using the (inverse) spin Hall effect as a means of detection. This is a necessary step to gather full understanding of the consequences of ...

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“…Further, a recent theoretical study showed the presence of a large R NL in Au-decorated graphene even in the absence of SOC [24]. They also reported that the spin Hall angle (θ SH ) in Au-clustered graphene can significantly fluctuate according to the applied gate voltage [24].…”

Section: Introductionmentioning

confidence: 95%

“…Kaverzin and van Wees also reported the absence of the field-induced effect in R NL for hydrogenated graphene and questioned the origin of previously reported R SHE NL [23]. Further, a recent theoretical study showed the presence of a large R NL in Au-decorated graphene even in the absence of SOC [24]. They also reported that the spin Hall angle (θ SH ) in Au-clustered graphene can significantly fluctuate according to the applied gate voltage [24].…”

Section: Introductionmentioning

confidence: 96%

Gate-dependent spin Hall induced nonlocal resistance and the symmetry of spin-orbit scattering in Au-clustered graphene

et al. 2017

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Engineering the electron dispersion of graphene to be spin-dependent is crucial for the realization of spin-based logic devices. Enhancing spin-orbit coupling in graphene can induce spin Hall effect, which can be adapted to generate or detect a spin current without a ferromagnet. Recently, both chemically and physically decorated graphenes have shown to exhibit large nonlocal resistance via the spin Hall and its inverse effects. However, these nonlocal transport results have raised critical debates due to the absence of field dependent Hanle curve in subsequent studies. Here, we introduce Au clusters on graphene to enhance spin-orbit coupling and employ a nonlocal geometry to study the spin Hall induced nonlocal resistance. Our results show that the nonlocal resistance highly depends on the applied gate voltage due to various current channels. However, the spin Hall induced nonlocal resistance becomes dominant at a particular carrier concentration, which is further confirmed through Hanle curves. The obtained spin Hall angle is as high as ∼0.09 at 2 K. Temperature dependence of spin relaxation time is governed by the symmetry of spin-orbit coupling, which also depends on the gate voltage: asymmetric near the charge neutral point and symmetric at high carrier concentration. These results inspire an effective method for generating spin currents in graphene and provide important insights for the spin Hall effect as well as the symmetry of spin scattering in physically decorated graphene.

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Spin Hall Effect and Origins of Nonlocal Resistance in Adatom-Decorated Graphene

Cited by 72 publications

References 76 publications

Model spin-orbit coupling Hamiltonians for graphene systems

Model spin-orbit coupling Hamiltonians for graphene systems

Spin precession and spin Hall effect in monolayer graphene/Pt nanostructures

Gate-dependent spin Hall induced nonlocal resistance and the symmetry of spin-orbit scattering in Au-clustered graphene

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