Scale-invariant large nonlocality in polycrystalline graphene

Ribeiro, Mário; Power, Stephen R.; Roche, Stephan; Hueso, Luis E.; Casanova, Fèlix

doi:10.1038/s41467-017-02346-x

Cited by 21 publications

(25 citation statements)

References 53 publications

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“…A similar asymmetry was recently observed and interpreted in Ref. [18] in terms of spin-dependent current at the grain boundaries of chemical-vapor-deposited graphene. The asymmetry could also be reproduced in our model if it is assumed that the conduction (of either edge or bulk states) depends on spin polarization.…”

Section: 37supporting

confidence: 87%

“…So far, the role of edge states when Landau levels are formed has not been mentioned. Nevertheless, their existence has been assumed in several similar experiments to explain the nonlocality [17][18][19]. It was also clearly observed that in clean samples, counterpropagating edge states are formed and lead to an insulating state under perpendicular magnetic field, which can start exhibiting well-quantized values when the relative spin contribution is increased under a tilted magnetic field [34].…”

Section: F Counterpropagating Edge Statesmentioning

confidence: 86%

“…The orange line corresponds to the spin diffusion model and is given by Eq. (2), assuming unrealistically high values θ sh = 1 and λ = 100 μm [18]. The thermoelectric contribution is given by the formula R 28,37 = (W/w)S 2 xy T /dκ xx , where W is the Hall bar width, w is the width of the lateral probes (W/w 5), d = 0.3 nm is the graphene thickness, κ xx is the thermal conductivity, and S xy is the Nernst coefficient.…”

Section: 37mentioning

confidence: 99%

“…The associated thermal gradient produces in turn a nonlocal voltage via the Nernst effect [11,16]. Second, theory does not predict counterpropagating edge states to be present at the CNP in the QHE (except for very clean samples); nevertheless, assuming their ad hoc existence allows reproducing quite well several experimental results, either in graphene [17,18] or in two-dimensional HgCdTe-based quantum wells [19], which have a very small gap and a band structure quite similar to graphene.…”

Section: Introductionmentioning

confidence: 99%

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Large nonlocality in macroscopic Hall bars made of epitaxial graphene

et al. 2018

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We report on nonlocal transport in large-scale epitaxial graphene on silicon carbide under an applied external magnetic field. The nonlocality is related to the emergence of the quantum Hall regime and persists up to the millimeter scale. The nonlocal resistance reaches values comparable to the local (Hall and longitudinal) resistances. At moderate magnetic fields, it is almost independent on the in-plane component of the magnetic field, which suggests that spin currents are not at play. The nonlocality cannot be explained by thermoelectric effects without assuming extraordinary large Nernst and Ettingshausen coefficients. A model based on counterpropagating edge states backscattered by the bulk reproduces quite well the experimental data.

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Section: 37supporting

confidence: 87%

Section: F Counterpropagating Edge Statesmentioning

confidence: 86%

Section: 37mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Large nonlocality in macroscopic Hall bars made of epitaxial graphene

et al. 2018

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“…In graphene, previous measurements of the SHE using nonlocal Hall bar geometries have been reported 15,16,20 . However, a variety of effects unrelated to spin can contribute to such nonlocal measurements, questioning the interpretation of the results and therefore impeding a further optimization and implementation of those spin effects into practical applications [68][69][70][71][72] . A convincing experimental proof of spin-to-charge conversion due to the SHE or the REE in graphene is thus crucially lacking.…”

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confidence: 99%

Room-Temperature Spin Hall Effect in Graphene/MoS₂ van der Waals Heterostructures

et al. 2019

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Graphene is an excellent material for long distance spin transport but allows little spin manipulation. Transition metal dichalcogenides imprint their strong spin-orbit coupling into graphene via proximity effect, and it has been predicted that efficient spin-to-charge conversion due to spin Hall and Rashba-Edelstein effects could be achieved. Here, by combining Hall probes with ferromagnetic electrodes, we unambiguously demonstrate experimentally spin Hall effect in graphene induced by MoS2 proximity and for varying temperature up to room temperature. The fact that spin transport and spin Hall effect occur in different parts of the same material gives rise to a hitherto unreported efficiency for the spinto-charge voltage output. Remarkably for a single graphene/MoS2 heterostructure-based device, we evidence a superimposed spin-to-charge current conversion that can be indistinguishably associated with either the proximity-induced Rashba-Edelstein effect in graphene or the spin Hall effect in MoS2. By comparing our results to theoretical calculations, the latter scenario is found the most plausible one. Our findings pave the way towards the combination of spin information transport and spin-to-charge conversion in two-dimensional materials, opening exciting opportunities in a variety of future spintronic applications.The efficient transport and the manipulation of spins in the same material are mutually exclusive as they would require simultaneously weak and strong spin-orbit coupling (SOC) respectively. Graphene, due to its low intrinsic SOC, is proven to be an outstanding material that can transport spins over long distance of tens of micrometres 1-10 . For the same reason, the generation and tuning of spin currents in graphene are out of reach, limiting its capability to active spintronic device functionalities and related applications. To solve this issue, methods to artificially induce SOC in graphene have been explored. For instance, the SOC in graphene has been enhanced by chemical doping [11][12][13][14][15][16][17] or by proximity-induced coupling with materials possessing large SOC [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] . The latter method is more convenient since the chemical properties of graphene are not altered, whereas its high-quality electronic transport properties are preserved.Transition metal dichalcogenides (TMDs) with chemical formula MX2 (M=Mo, W and X=S, Se) are layered materials of semiconducting nature displaying unique combined electronic, optical, spintronic and valleytronic properties [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] . They possess a strong intrinsic SOC of tens of meV, few orders larger than that of pristine graphene 36,37 . Accordingly, a large intrinsic spin Hall effect (SHE) has been theoretically predicted in TMDs 38 . However, its experimental observation remains elusive because of the technical difficulties to inject and detect spin information into these materials 49,50 . Only recently, a spin-orbit torque experim...

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Graphene on Chromia: A System for Beyond‐Room‐Temperature Spintronics

Barut

Yin

et al. 2022

Advanced Materials

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potential of this 2D material for spintronic applications. The weak spin relaxation in graphene can be ascribed to its vanishingly small native spin-orbit coupling [13][14][15][16] (SOC), a property that makes the manipulation of spins in the same material challenging. [4] To resolve this conundrum, various strategies have been explored to introduce magnetic character into graphene, most notably by exploiting proximity effects at its interface with an appropriate magnetic substrate. [17][18][19][20][21][22][23][24] The development of functional room-temperature devices based upon such heterostructures remains an ongoing challenge.Another approach to enhancing SOC in graphene relies on breaking the sublattice symmetry of its pristine crystal. [25,26] By opening a gap between the conduction and valence bands, this distortion effectively adds a SOC term to the Hamiltonian of graphene. In one such approach, hydrogenation has been used to induce sp 2 -to-sp 3 bond conversion, causing a buckling of the graphene structure that yields clear signatures of spin transport at room temperature. [27] Symmetry breaking has also been achieved by supporting graphene on a variety of non-magnetic substrates, such as SiC, [28] Al 2 O 3 , [29] MgO, [30] and BN. [31] While these approaches have their advantages, none of them offer the non-volatility desired to imbue spintronic devices with a potential edge over CMOS. [32] Herein, we describe an approach to achieving robust spindependent transport in graphene, well beyond room temperature, that we realize by supporting this two-dimensional material on a substrate comprised of an antiferromagnetic (AFM) oxide (chromia, Cr 2 O 3 ). One of a small number of materials to exhibit magneto-electric (ME) nature (i.e., coupling of magnetic and electrostatic polarizations) at room temperature (and beyond), [33,34] chromia is antiferromagnetic (AFM) in bulk but exhibits a net alignment of magnetic moments at its (0001) surface. [33,[35][36][37] This boundary magnetism allows chromia to function as a highly spin-polarized substrate, which is ideally suited for combination with a graphene overlayer. [32,38] The excellent dielectric character [39,40] of chromia, along with its ME nature, allows an applied voltage to be used to reverse the direction of its boundary magnetization, at significantly lower energy cost (≈aJ) than that associated with the current-driven switching of ferromagnets. [32] Evidence of robust spin-dependent transport in monolayer graphene, deposited on the (0001) surface of the antiferromagnetic (AFM)/magneto-electric oxide chromia (Cr 2 O 3 ), is provided. Measurements performed in the non-local spin-Hall geometry reveal a robust signal that is present at zero external magnetic field and which is significantly larger than any possible ohmic contribution. The spin-related signal persists well beyond the Néel temperature (≈307 K) that defines the transition between the AFM and paramagnetic states, remaining visible at the highest studied temperature of close to 450 K. This robust...

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Scale-invariant large nonlocality in polycrystalline graphene

Cited by 21 publications

References 53 publications

Large nonlocality in macroscopic Hall bars made of epitaxial graphene

Large nonlocality in macroscopic Hall bars made of epitaxial graphene

Room-Temperature Spin Hall Effect in Graphene/MoS₂ van der Waals Heterostructures

Graphene on Chromia: A System for Beyond‐Room‐Temperature Spintronics

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Scale-invariant large nonlocality in polycrystalline graphene

Cited by 21 publications

References 53 publications

Large nonlocality in macroscopic Hall bars made of epitaxial graphene

Large nonlocality in macroscopic Hall bars made of epitaxial graphene

Room-Temperature Spin Hall Effect in Graphene/MoS2 van der Waals Heterostructures

Graphene on Chromia: A System for Beyond‐Room‐Temperature Spintronics

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Product

Resources

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Room-Temperature Spin Hall Effect in Graphene/MoS₂ van der Waals Heterostructures