Valley-based field-effect transistors in graphene

Lee, M.-K.; Lue, Ning-Yuan; Wen, Chong-Shian; Wu, George

doi:10.1103/physrevb.86.165411

Cited by 39 publications

(19 citation statements)

References 22 publications

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“…Likewise, charge carriers in two-dimensional (2D) hexagonal crystals have an additional electronic degree of freedom, the valley-index, associated to degenerate bands at the inequivalent K and K' points in the Brillouin Zone (BZ). The valleytronic field proposes the creation of a new class of dissipationless electronic devices based on the manipulation of the valley-indices like valley filters and valley valves [1,10,11,12]. One interesting 2D crystal with useful features for valleytronics is BLG.…”

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confidence: 99%

Topological valley transport at the curved boundary of a folded bilayer graphene

et al. 2019

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The development of valleytronics demands long-range electronic transport with preserved valley index, a degree of freedom similar to electron spin. A promising structure for this end is a topological one-dimensional (1D) channel formed in bilayer graphene (BLG) under special electrostatic conditions or specific stacking configuration, called domain wall (DW) [1, 2, 3, 4, 5]. In these 1D channels, the valley-index defines the propagation direction of the charge carriers and the chiral edge states (kink states) are robust over many kinds of disorder [3]. However, the fabrication of DWs is challenging, requiring the design of complex multi-gate structures [6, 7] or have been producing on rough substrates [8, 9], showing a limited mean 1 arXiv:1901.08178v1 [cond-mat.mes-hall] 24 Jan 2019 free path. Here, we report on a high-quality DW formed at the curved boundary of folded bilayer graphene (folded-BLG). At such 1D conducting channel we measured a two-terminal resistance close to the quantum resistance R = e 2 /4h at zero magnetic field, a signature of kink states. Our experiments reveal a long-range ballistic transport regime that occurs only at the DW of the folded-BLG, while the other regions behave like semiconductors with tunable band gap.Electric charge and spin are intrinsic quantum properties of electrons and so far, are the basis of electronics. Likewise, charge carriers in two-dimensional (2D) hexagonal crystals have an additional electronic degree of freedom, the valley-index, associated to degenerate bands at the inequivalent K and K' points in the Brillouin Zone (BZ). The valleytronic field proposes the creation of a new class of dissipationless electronic devices based on the manipulation of the valley-indices like valley filters and valley valves [1,10,11,12]. One interesting 2D crystal with useful features for valleytronics is BLG. The material is a tunable semiconductor and contains low lattice defects that prevents inter-valley scattering. Moreover, it holds topological properties when its inversion symmetry is broken by the application of transverse electric field. In this condition, a topological invariant is defined, the integer index called Chern number, with important implications on the quantum properties of BLG. For instance, it gives rise to the observation of the valley Hall Effect in graphene [13,14,15], which is a topological phase where gapless edge states labelled by opposite valley-indices counter-propagate at the boundaries of the insulating bulk [16]. One important aspect of the Chern number in BLG is that its sign depends either on the valley-index as well as on the sign of the band gap (interlayer energy difference), which can be changed by inverting the electric field direction or by inverting the stacking order of the material [16, 1, 2, 3, 5].Such control of the band gap of BLG allows the design of topological 1D interfaces between regions with opposite Chern numbers -a domain wall -where strongly confined edge states 2 called kink states are predicted [1, 2, 3, 4, 5]. The...

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Topological valley transport at the curved boundary of a folded bilayer graphene

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“…Our results may be also relevant for spin transistors built with two-dimensional electron systems other than semiconductor heterostructures: silicon [69,70], graphene [60,[71][72][73][74] or metal dichalcogenides [74]. Further extensions of our model should consider the quasione-dimensional case, which is important for quantum wires and carbon nanotubes.…”

Section: Discussionmentioning

confidence: 89%

Seebeck effects in two-dimensional spin transistors

2015

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We consider a spin-orbit-coupled two-dimensional electron system under the influence of a thermal gradient externally applied to two attached reservoirs. We discuss the generated voltage bias (charge Seebeck effect), spin bias (spin Seebeck effect) and magnetization-dependent thermopower (magneto-Seebeck effect) in the ballistic regime of transport at linear response. We find that the charge thermopower is an oscillating function of both the spin-orbit strength and the quantum well width. We also observe that it is always negative for normal leads. We carefully compare the exact results for the linear response coefficients and a Sommerfeld approximation. When the contacts are ferromagnetic, we calculate the spin-resolved Seebeck coefficient for parallel and antiparallel magnetization configuration. Remarkably, the thermopower can change its sign by tuning the Fermi energy. This effect disappears when the Rashba coupling is absent. Additionally, we determine the magneto-Seebeck ratio, which shows dramatic changes in the presence of a the Rashba potential.

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“…This leads to the valley precession of channel electrons in the valley space [12]. The valley precession in graphene is the basis for the valley field effect transistor [8]. And the valley precession can also be characterized by a valley pseudomagnetoresistance (VPMR) in the FM-S/Kek-Y/FM-S junctions, analogous to the magnetoresistance in graphene-based quantum tunneling junctions with the spin-orbit interaction [4], which is defined as VPMR = G P −G AP G P…”

Section: Methodsmentioning

confidence: 99%

“…Owing to the large momentum difference between the two valleys and the suppression of the intervalley scattering in clean graphene samples [5][6][7], the valley degree of freedom is believed to exert the same effect as the electron spin in carrying and manipulating information, which leads to a new discipline rising as valleytronics. In analog of spin field-effect transistor, valley field-effect transistor is also theoretically proposed in graphene [8], which consists of a quantum one dimension channel of gapped graphene sandwiched between two armchair graphene nanoribbons (source and drain); then, side gate electric field is applied to the channel and modulates the valley polarization of carriers due to the valley-orbit interaction, thus controlling the amount of current collected at the drain. However, due to the fact that the valley coupling in graphene has not become a physical reality for a long time, there are few further studies based on the valley field-effect transistors of graphene and related studies.…”

Section: Introductionmentioning

confidence: 99%

Electric-Controlled Valley Pseudomagnetoresistance in Graphene with Y-Shaped Kekulé Lattice Distortion

Chang

Yu-zeng

et al. 2020

Nanoscale Res Lett

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We propose a new method for regulating valley pseudomagnetoresistance in ballistic graphene-based valley fieldeffect transistors by taking into account the Y-shaped Kekulé lattice distortion and electric barrier. The device involves valley injection and valley detection by ferromagnetic-strain source and drain. The valley manipulation in the channel is achieved via the Y-shaped Kekulé lattice distortion and electric barrier. The central mechanism of these devices lies on Y-shaped Kekulé lattice distortion in graphene can induce a valley precession, thus controlling the valley orientation of channel electrons and hence the current collected at the drain. We found that the tuning external bias voltage makes the valley pseudomagnetoresistance oscillate between positive and negative values and colossal tunneling valley pseudomagnetoresistance of over 30,000% can be achieved. Our results suggest that the synergy of valleytronics and digital logics may provide new paradigms for valleytronic-based information processing and reversible computing.

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Valley-based field-effect transistors in graphene

Cited by 39 publications

References 22 publications

Topological valley transport at the curved boundary of a folded bilayer graphene

Topological valley transport at the curved boundary of a folded bilayer graphene

Seebeck effects in two-dimensional spin transistors

Electric-Controlled Valley Pseudomagnetoresistance in Graphene with Y-Shaped Kekulé Lattice Distortion

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