<i>Ab initio</i>spin-flip conductance of hydrogenated graphene nanoribbons: Spin-orbit interaction and scattering with local impurity spins

Wilhelm, Jan; Walz, Michael; Evers, Ferdinand

doi:10.1103/physrevb.92.014405

Cited by 42 publications

(48 citation statements)

References 88 publications

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“…[15][16][17][18][19][20][21] This vast discrepancy can be reliably explained assuming a small amount (orders of ppm) of resonant magnetic scatters [22][23][24] like for example hydrogen atoms 25,26 or vacancies. 26,27 Related theoretical studies [28][29][30] confirmed that magnetic moments, indeed, strongly affect spin dynamics and can cause the ultra-fast spin relaxation. A recent experiment of the Valenzuela group [31], analyzing graphene's spin-lifetime anisotropy, supports that view and convincingly rules out SOC as a determining factor of the fast spin relaxation.…”

Section: Introductionmentioning

confidence: 95%

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: 95%

Model spin-orbit coupling Hamiltonians for graphene systems

2017

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“…One way to enhance these interactions is by functionalizing graphene with adatoms and admolecules, which works well for both exchange [2][3][4][5][6][7] and spin-orbit [7][8][9][10][11][12][13][14][15][16] couplings. Functionalized graphene has local "hot spots" of giant exchange and spin-orbit fields, which can be used to investigate spin transport [17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Theory of proximity-induced exchange coupling in graphene on hBN/(Co, Ni)

et al. 2016

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Graphene, being essentially a surface, can borrow some properties of an insulating substrate (such as exchange or spin-orbit couplings) while still preserving a great degree of autonomy of its electronic structure. Such derived properties are commonly labeled as proximity. Here we perform systematic first-principles calculations of the proximity exchange coupling, induced by cobalt (Co) and nickel (Ni) in graphene, via a few (up to three) layers of hexagonal boron nitride (hBN). We find that the induced spin splitting of the graphene bands is of the order of 10 meV for a monolayer of hBN, decreasing in magnitude but alternating in sign by adding each new insulating layer. We find that the proximity exchange can be giant if there is a resonant d level of the transition metal close to the Dirac point. Our calculations suggest that this effect could be present in Co heterostructures, in which a d level strongly hybridizes with the valence-band orbitals of graphene. Since this hybridization is spin dependent, the proximity spin splitting is unusually large, about 10 meV even for two layers of hBN. An external electric field can change the offset of the graphene and transition-metal orbitals and can lead to a reversal of the sign of the exchange parameter. This we predict to happen for the case of two monolayers of hBN, enabling electrical control of proximity spin polarization (but also spin injection) in graphene/hBN/Co structures. Nickel-based heterostructures show weaker proximity effects than cobalt heterostructures. We introduce two phenomenological models to describe the first-principles data. The minimal model comprises the graphene (effective) p z orbitals and can be used to study transport in graphene with proximity exchange, while the p z -d model also includes hybridization with d orbitals, which is important to capture the giant proximity exchange. Crucial to both models is the pseudospin-dependent exchange coupling, needed to describe the different spin splittings of the valence and conduction bands.

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“…This is important since CVD-grown graphene contains extended edgelike defects in the form of grain boundaries [25][26][27][28], unlike bottom-up approaches which may allow the synthesis of more precise geometries [29]. We are further motivated by the strong dependence of GNR transport on edge geometry and impurity distribution [30][31][32][33][34][35][36][37][38][39][40][41][42][43] and by sublattice dependent features in carbon nanotubes [44,45]. We consider both armchair-(AGNR) and zigzag-(ZGNR) edged ribbons, noting the in-built sublattice asymmetry of ZGNRs due to sites along one edge belonging to one sublattice.…”

Section: Introductionmentioning

confidence: 99%

Electronic transport in graphene nanoribbons with sublattice-asymmetric doping

2016

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Recent experimental findings and theoretical predictions suggest that nitrogen-doped CVD-grown graphene may give rise to electronic band gaps due to impurity distributions which favour segregation on a single sublattice. Here we demonstrate theoretically that such distributions lead to more complex behaviour in the presence of edges, where geometry determines whether electrons in the sample view the impurities as a gap-opening average potential or as scatterers. Zigzag edges give rise to the latter case, and remove the electronic bandgaps predicted in extended graphene samples. We predict that such behaviour will give rise to leakage near grain boundaries with a similar geometry or in zigzag-edged etched devices. Furthermore, we examine the formation of one-dimensional metallic channels at interfaces between different sublattice domains, which should be observable experimentally and offer intriguing waveguiding possibilities.

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Ab initiospin-flip conductance of hydrogenated graphene nanoribbons: Spin-orbit interaction and scattering with local impurity spins

Cited by 42 publications

References 88 publications

Model spin-orbit coupling Hamiltonians for graphene systems

Model spin-orbit coupling Hamiltonians for graphene systems

Theory of proximity-induced exchange coupling in graphene on hBN/(Co, Ni)

Electronic transport in graphene nanoribbons with sublattice-asymmetric doping

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