Valley Filtering and Electronic Optics Using Polycrystalline Graphene

Nguyễn, Việt Hùng; Dechamps, Samuel; Dollfus, Philippe; Charlier, Jean‐Christophe

doi:10.1103/physrevlett.117.247702

Cited by 51 publications

(59 citation statements)

References 56 publications

(84 reference statements)

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“…A graphene p-n junction is a negative refraction interface for electrons [1], which was recently verified in transport experiment [2]. The unusually refraction, with considering the factors such as spin, valley, strain, and band warping, results in a variety of refraction and focusing effects [4,3,[5][6][7][8]. In a strained graphene channel, the Fabry-Pérot states can carry a pure valley current [9].…”

Section: Introductionmentioning

confidence: 86%

Vortex of beam shift induced by mono-chiral interface states

2020

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If an electron beam hits onto the interface of a Weyl-node-mismatch junction, a shift of the beam center on the interface happens when the beam is reflected or transmitted, where the junction consists of two materials of the same Weyl semimetal and one of them is rotated with respect to the other by an angle. We calculate the longitudinal and transverse shift components (the Goos-Hänchen and Imbert-Fedorov shifts). The reflection shift for total reflection cases is much more remarkable than the shift for transmitted cases. There exists a semi-vortex structure of the reflection shift on the inplane k-space. The vortex is induced by the touch between bulk bands and interface bands. The formation of such interface bands is explained by the pulley-group model, in which the Weyl cones serve as wheels and the surface and interface bands act as ropes. A surface rope connects wheels of opposite chiralities, and an interface rope links the wheels for the two side materials of the same chirality.

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Section: Introductionmentioning

confidence: 86%

Vortex of beam shift induced by mono-chiral interface states

2020

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“…In analogy to the intrinsic spin Hall effect, VHE of the intrinsic type was subsequently proposed through the introduction of a staggered sublattice potential to generate finite valley-contrasting Berry curvatures 2,13 . Extrinsic VHE requires external valley-resolved perturbations such as magnetic fields, strain-induced pseudo magnetic fields, or magnetic materials that have opposite effect on the two valleys 10,11,[18][19][20] . However, our gVHE is distinct and can arise in the absence of non-trivial Berry curvatures and any external valley-dependent perturbation.…”

Section: Appendix F: Extrinsic Versus Intrinsic Valley Hall Effectmentioning

confidence: 99%

“…In addition to charge and spin, valley quantum numbers provide an alternative way to distinguish and designate quantum states, leading to the concept of valleytronics 1,2 , an area that has attracted much recent interest [3][4][5][6][7][8][9][10][11] . Take graphene as an example, where the crystalline structure stipulates that uncharged degrees of freedom such as valley isospin can arise 12 .…”

Section: Introductionmentioning

confidence: 99%

“…In graphene, due to its synthetic nature, the valley isospin can be manipulated for various valley filtering designs via strategies such as perfect zigzag edge confinements 1 , staggered sublattice potentials 2 , trigonal warping effect of the band structures 15 , line defects 17 , and strain engineering 10,11,[18][19][20] . A viable mechanism to realize valley filtering is through the valley Hall effect (VHE) 2,5,7,[21][22][23][24][25][26][27][28] , where electrons with different valley quantum numbers are separated and move in spatially distinct regions.…”

Section: Introductionmentioning

confidence: 99%

“…Alternative mechanisms for VHE require external magnetic fields, strain-induced pseudo magnetic fields, or magnetic materials that have an opposite effect on the two valleys 10,11,[18][19][20] . We ask the following question: when Berry curvatures vanish does nontrivial valleycontrasting physics exist without any valley-resolved perturbation?…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Geometric valley Hall effect and valley filtering through a singular Berry flux

Huang

et al. 2017

Phys. Rev. B

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Conventionally, a basic requirement to generate valley Hall effect (VHE) is that the Berry curvature for conducting carriers in the momentum space be finite so as to generate anomalous deflections of the carriers originated from distinct valleys into different directions. We uncover a geometric valley Hall effect (gVHE) in which the valley-contrasting Berry curvature for carriers vanishes completely except for the singular points. The underlying physics is a singular non-π fractional Berry flux located at each conical intersection point in the momentum space, analogous to the classic AharonovBohm effect of a confined magnetic flux in real space. We demonstrate that, associated with gVHE, exceptional skew scattering of valley-contrasting quasiparticles from a valley-independent, scalar type of impurities can generate charge neutral, transverse valley currents. As a result, the massless nature of the quasiparticles and their high mobility are retained. We further demonstrate that, for the particular Berry flux of π/2, gVHE is considerably enhanced about the skew scattering resonance, which is electrically controllable. A remarkable phenomenon of significant practical interest is that, associated with gVHE, highly efficient valley filtering can arise. These phenomena are robust against thermal fluctuations and disorders, making them promising for valleytronics applications.

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Electrically Tunable Spin Exchange Splitting in Graphene Hybrid Heterostructure

Shin,

Kim,

Hong

et al. 2023

Adv Funct Materials

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Graphene, with spin and valley degrees of freedom, fosters unexpected physical and chemical properties for the realization of next‐generation quantum devices. However, the spin‐symmetry of graphene is rather robustly protected, hampering manipulation of the spin degrees of freedom for the application of spintronic devices such as electric gate‐tunable spin filters. It is demonstrated that a hybrid heterostructure composed of graphene and LaCoO3 epitaxial thin film exhibits an electrically tunable spin‐exchange splitting. The large and adjustable spin‐exchange splitting of 155.9 – 306.5 meV is obtained by the characteristic shifts in both the spin‐symmetry‐broken quantum Hall states and the Shubnikov–de Haas oscillations. Strong hybridization‐induced charge transfer across the hybrid heterointerface has been identified for the observed spin exchange splitting. The substantial and facile controllability of the spin exchange splitting provides an opportunity for spintronics applications with the electrically‐tunable spin polarization in hybrid heterostructures.

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Valley Filtering and Electronic Optics Using Polycrystalline Graphene

Cited by 51 publications

References 56 publications

Vortex of beam shift induced by mono-chiral interface states

Vortex of beam shift induced by mono-chiral interface states

Geometric valley Hall effect and valley filtering through a singular Berry flux

Electrically Tunable Spin Exchange Splitting in Graphene Hybrid Heterostructure

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