Generalized tight-binding transport model for graphene nanoribbon-based systems

Hancock, Yvette; Uppstu, Andreas; Saloriutta, Karri; Harju, Ari; Puska, Martti J.

doi:10.1103/physrevb.81.245402

Cited by 147 publications

(125 citation statements)

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“…We stress that so long as signum(U N ) = signum(U B ), the precise values of the tight binding parameters do not make any difference to the overall topological properties of the system, and merely give small quantitative changes to the band structure and hence the exact positions of the conductance steps. In principle, a more accurate description of the band structure of the ribbons is given by a third-nearest neighbour tight binding theory [22,23], but this additional complexity changes none of the qualitative features of the results, or the considerations about the topology of the system. Therefore, we restrict our discussion to the nearest neighbour model for clarity.…”

Section: Methodsmentioning

confidence: 99%

Robustness of topologically protected transport in graphene–boron nitride lateral heterostructures

Abergel

2016

J. Phys.: Condens. Matter

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Abstract. Previously, graphene nanoribbons set in lateral heterostructures with hexagonal boron nitride were predicted to support topologically protected states at low energy. We investigate how robust the transport properties of these states are against lattice disorder. We find that forms of disorder that do not couple the two valleys of the zigzag graphene nanoribbon do not impact the transport properties at low bias, indicating that these lateral heterostructures are very promising candidates for chipscale conducting interconnects. Forms of disorder that do couple the two valleys, such as vacancies in the graphene ribbon, or substantial inclusions of armchair edges at the graphene-hexagonal boron nitride interface will negatively affect the transport. However, these forms of disorder are not commonly seen in current experiments.

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Section: Methodsmentioning

confidence: 99%

Robustness of topologically protected transport in graphene–boron nitride lateral heterostructures

Abergel

2016

J. Phys.: Condens. Matter

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“…We use the parameters t 1 = −2.7 eV, t 2 = −0.2 eV, and t 3 = −0.18 eV, between sites that are first, second, and third-nearest neighbors, and the Hubbard on-site interaction parameter is U = 2 eV. 22 The many-body calculation utilizes the Lanczos algorithm to solve ∼100 lowest many-body eigenstates accurately. The state space is formed from a given symmetry sector by constructing many-body configurations of tight-binding orbitals, and by ordering them according to the energy of the tight-binding part of the Hamiltonian.…”

Section: Methodsmentioning

confidence: 99%

Electronic states in finite graphene nanoribbons: Effect of charging and defects

et al. 2013

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Ijäs, M.; Ervasti, M.; Uppstu, Christer; Liljeroth, Peter; van der Lit, J.; Swart, I.; Harju, A. We study the electronic structure of finite armchair graphene nanoribbons using density-functional theory and the Hubbard model, concentrating on the states localized at the zigzag termini. We show that the energy gaps between end-localized states are sensitive to doping, and that in doped systems, the gap between the end-localized states decreases exponentially as a function of the ribbon length. Doping also quenches the antiferromagnetic coupling between the end-localized states leading to a spin-split gap in neutral ribbons. By comparing dI/dV maps calculated using the many-body Hubbard model, its mean-field approximation and density-functional theory, we show that the use of a single-particle description is justified for graphene π states in case spin properties are not the main interest. Furthermore, we study the effect of structural defects in the ribbons on their electronic structure. Defects at one ribbon terminus do not significantly modify the electronic states localized at the intact end. This provides further evidence for the interpretation of a multipeak structure in a recent scanning tunneling spectroscopy (STS) experiment resulting from inelastic tunneling processes [van der Lit et al., Nat. Commun. 4, 2023]. Finally, we show that the hydrogen termination at the flake edges leaves identifiable fingerprints on the positive bias side of STS measurements, thus possibly aiding the experimental identification of graphene structures. Electronic states in finite graphene nanoribbons: Effect of charging and defects

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“…For instance, in GNRs with zigzag edges, electronic transport is dominated by edge states which have been observed in scanning tunneling microscopy [4]. These states are expected to be spin-polarized and make zigzag-edge GNR (ZGNR) junctions attractive for nanoscale spintronic applications such as spin filters [5][6][7][8][9][10][11][12]. In order to achieve a spintronic device, it is very important to find nonmagnetic materials where a spin-polarized current can be injected and flowed without becoming depolarized.…”

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confidence: 99%

A spin-filter device based on armchair graphene nanoribbons

Saffarzadeh

Farghadan

2011

Applied Physics Letters

114

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The coherent spin-polarized electron transport through a zigzag-edge graphene flake (ZGF), sandwiched between two semi-infinite armchair graphene nanoribbons, is investigated by means of Landauer-Buttiker formalism. To study the edge magnetism of the ZGF, we use the half-filled Hubbard model within the Hartree-Fock approximation. The results show that the junction acts as a spin filter with high degree of spin polarization in the absence of magnetic electrodes and external fields. By applying a gate voltage the spin-filtering efficiency of this device can be effectively controlled and the spin polarization can reach values as high as 90%.Graphene nanoribbons (GNRs) and graphene junctions are good candidates for electronic and spintronic devices due to high carrier mobility, long spin-relaxation times and lengths, and spin-filtering effect [1][2][3]. In fact, the conduction electrons in carbon-based materials can move very long distances without scattering due to their small spin-orbit coupling and low hyperfine interaction. For instance, in GNRs with zigzag edges, electronic transport is dominated by edge states which have been observed in scanning tunneling microscopy [4]. These states are expected to be spin-polarized and make zigzag-edge GNR (ZGNR) junctions attractive for nanoscale spintronic applications such as spin filters [5][6][7][8][9][10][11][12]. In order to achieve a spintronic device, it is very important to find nonmagnetic materials where a spin-polarized current can be injected and flowed without becoming depolarized. The ground state of ZGNRs has an antiferromagnetic spin configuration where the total spin (S) is zero. However, when the system has different number of A-and B-sublattice sites, the total spin of the ground state is 2S = N A − N B [13] and by appropriate designing, one can form a ferromagnetic spin configuration at the zigzag edges. Most of the previous studies on spinfiltering effects have been focused on the junctions, which consist of ZGNR electrodes.In this letter, a GNR junction which operates as a spin-filter in the absence of an external electric field is presented and the influence of edge atoms on spin transport through the junction will be examined. We also investigate the sensitivity of the spin polarization to the gate voltage to obtain a maximum value for this polarization. An interesting feature of our system is that, in spite of the previous studies, the type of electrodes in this junction is armchair-edge GNR and the central part of the system is a zigzag-edge graphene nanodisk [6,14], as shown in Fig. 1(a). In this junction, the right GNR electrode with a ribbon index n=8 has a width W R =0.86 nm, while the left electrode with a ribbon index n=33 * Electronic address: a-saffar@tpnu.ac.ir has a width W L =3.93 nm. Furthermore, the central region (nanodisk) with a trapezoidal shape consists of N C = 240 carbon atoms and produces a ferromagnetic spin configuration at its edges.We simulate the system depicted in Fig. 1(a) by use of a single-band tight-binding model an...

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Generalized tight-binding transport model for graphene nanoribbon-based systems

Cited by 147 publications

References 29 publications

Robustness of topologically protected transport in graphene–boron nitride lateral heterostructures

Robustness of topologically protected transport in graphene–boron nitride lateral heterostructures

Electronic states in finite graphene nanoribbons: Effect of charging and defects

A spin-filter device based on armchair graphene nanoribbons

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