Charge, Spin and Valley Hall Effects in Disordered Graphene

Cresti, Alessandro; Nikolić, Branislav K.; García, Jose Hugo; Roche, Stephan

doi:10.48550/arxiv.1610.09917

Cited by 2 publications

(4 citation statements)

References 259 publications

(554 reference statements)

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“…Bilayer graphene is however more chemically stable and easier to integrate in electronic devices, and it further allows tailoring proximity effects by properly choosing the substrates or twist angles between layers. Our simulations reveal that the edge states are strongly robust to both bulk and edge disorders, therefore offering a way to create persistent valley-polarized currents, in contrast to the vast majority of valley-related phenomena where valley currents are fragile and very sensitive to short-range scatterers [86]. Both the valleypolarization and chirality of the VP-QAHE can be reversed by changing the magnetization of the magnetic material, and a perpendicular electric field drives the topological phase transition.…”

mentioning

confidence: 86%

Valley-Polarized Quantum Anomalous Hall Phase in Bilayer Graphene with Layer-Dependent Proximity Effects

Vila,

Garcia,

Roche

2021

Preprint

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Realizations of some topological phases in two-dimensional systems rely on the challenge of jointly incorporating spin-orbit and magnetic exchange interactions. Here, we predict the formation and control of a fully valley-polarized quantum anomalous Hall effect in bilayer graphene, by separately imprinting spin-orbit and magnetic proximity effects in different layers. This results in varying spin splittings for the conduction and valence bands, which gives rise to a topological gap at a single Dirac cone. The topological phase can be controlled by a gate voltage and switched between valleys by reversing the sign of the exchange interaction. By performing quantum transport calculations in disordered systems, the chirality and resilience of the valley-polarized edge state are demonstrated. Our findings provide a promising route to engineer a topological phase that could enable low-power electronic devices and valleytronic applications.

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confidence: 86%

Valley-Polarized Quantum Anomalous Hall Phase in Bilayer Graphene with Layer-Dependent Proximity Effects

Vila,

Garcia,

Roche

2021

Preprint

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“…In the case of spin-splitting, incoming currents can be directed into output leads according to their spin orientation. Such behavior is analogous to the spin Hall effect 38 , but without relying on spin-orbit coupling (SOC) effects. These features were shown to be robust against disorder, unlike those in other antidot geometries, due to their dependence on local symmetry breaking effects and cumulative scattering from multi-ple antidots, and not on the exact separation and size of perforations.…”

Section: Introductionmentioning

confidence: 92%

“…(2) where E the Fermi energy, G + (H, ε) the advanced Green's function, δ(x) the Dirac's delta function and v α ≡ [H, X α ]/i the α-component of the velocity operator. The off-diagonal elements are computed numerically by using an efficient linear-scaling algorithm based on the kernel polynomial method 38,51 . For the diagonal elements, Eq.…”

Section: Geometry and Modelmentioning

confidence: 99%

“…Disordered systems, containing millions of atoms and hundreds of structural perforations, are simulated using a combination of mean-field Hubbard approaches for individual zz-TGAs and large-scale quantum transport methods to study composite systems. The electronic behavior is analysed using the Chebyshev expansion of the density of states (DOS) 45,46 , while the longitudinal [47][48][49][50] and transverse 38,51,52 conductivities are computed using the Kubo-Greenwood formalism. The Kubo method gives direct access to both the diagonal conductivities σ xx and σ yy , from which the charge transport anisotropy σ yy /σ xx can be measured, and the off-diagonal conductivities σ xy , which can be connected to measurements of the spin Hall effect.…”

Section: Introductionmentioning

confidence: 99%

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Charge and spin transport anisotropy in nanopatterned graphene

et al. 2018

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Anisotropic electronic transport is a possible route towards nanoscale circuitry design, particularly in two-dimensional materials. Proposals to introduce such a feature in patterned graphene have to date relied on large-scale structural inhomogeneities. Here we theoretically explore how a random, yet homogeneous, distribution of zigzag-edged triangular perforations can generate spatial anisotropies in both charge and spin transport. Anisotropic electronic transport is found to persist under considerable disordering of the perforation edges, suggesting its viability under realistic experimental conditions. Furthermore, controlling the relative orientation of perforations enables spin filtering of the transmitted electrons, resulting in a half-metallic anisotropic transport regime. Our findings point towards a co-integration of charge and spin control in a two-dimensional platform of relevance for nanocircuit design. We further highlight how geometrical effects allow finite samples to display finite transverse resistances, reminiscent of Spin Hall effects, in the absence of any bulk fingerprints of such mechanisms, and explore the underlying symmetries behind this behaviour. approach based on uniformly distributed perforations, where the anisotropic behavior is dictated by the atomiclevel properties of the perforation edges.Extended edges with the zigzag (zz) geometry locally break sublattice symmetry, leading to the formation of localized states [21,22], and to the formation of local magnetic moments when electron-electron interactions are considered [23][24][25][26][27]. Local moments of opposite sign occur at the edges associated with different sublattices, so that global ferromagnetism can only occur when the overall sublattice symmetry is broken [23,28,29], in accordance with Lieb's theorem [30]. This does not occur for zz-edged nanoribbons [31] or perforations containing edges equally divided between the sublattices [32]. However, the three edges of a zz-edged triangular graphene antidot (zz-TGA) are all associated with a single sublattice, which dictates large ferromagnetic moments [8, 33-37] (see figure 1).Recent works have demonstrated that lattices of approximately 1 nm side length zz-TGAs provide an excellent platform for electronic and spintronic applications due to robust band gaps, half-metallicity, and spinsplitting properties [8,9]. In the case of spin-splitting, incoming currents can be directed into output leads according to their spin orientation. Such behavior is analogous to the spin Hall effect [38], but without relying on spin-orbit coupling (SOC) effects. These features were shown to be robust against disorder, unlike those in other antidot geometries, due to their dependence on local symmetry breaking effects and cumulative scattering from multiple antidots, and not on the exact separation and size of perforations. With state-of-the-art lithographic methods, triangular holes in graphene [39], as well as zz-etched nanostructures [40][41][42], can be realised. Alternatively, a patterned laye...

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Charge, Spin and Valley Hall Effects in Disordered Graphene

Cited by 2 publications

References 259 publications

Valley-Polarized Quantum Anomalous Hall Phase in Bilayer Graphene with Layer-Dependent Proximity Effects

Valley-Polarized Quantum Anomalous Hall Phase in Bilayer Graphene with Layer-Dependent Proximity Effects

Charge and spin transport anisotropy in nanopatterned graphene

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