Fully Valley-Polarized Electron Beams in Graphene

Garcia‐Pomar, Juan Luis; Cortijo, Alberto; Nieto‐Vesperinas, M.

doi:10.1103/physrevlett.100.236801

Cited by 231 publications

(191 citation statements)

References 21 publications

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“…The original proposal to create and detect valley polarization relies on edge effects; 12 alternative proposals employ broken sublattice symmetry combined with in-plane electric fields 14 or drastic doping. 15 Besides the practical obstacles to implement these routes, these proposals face the severe problem of strong intervalley scattering occurring at pn junctions in monolayer graphene. 16 In this context, the valley-dependent helical scattering offers two key advantages: The required interfaces can be implemented and controlled by ordinary gates, and intervalley scattering is negligible.…”

Section: Introductionmentioning

confidence: 99%

Helical scattering and valleytronics in bilayer graphene

Schomerus

2010

Phys. Rev. B

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We describe an angularly asymmetric interface-scattering mechanism which allows to spatially separate the electrons in the two low-energy valleys of bilayer graphene. The effect occurs at electrostatically defined interfaces separating regions of different pseudospin polarization, and is associated with the helical winding of the pseudospin vector across the interface, which breaks the reflection symmetry in each valley. Electrons are transmitted with a preferred direction of up to 60°over a large energetic range in one of the valleys, and down to −60°in the other. In a Y-junction geometry, this can be used to create and detect valley polarization.

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Section: Introductionmentioning

confidence: 99%

Helical scattering and valleytronics in bilayer graphene

Schomerus

2010

Phys. Rev. B

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“…Predictions for electrons in graphene that make use of these valleys, e.g., a valleypolarized beam splitter [12], are difficult to realize since the coupling of electron wave functions to different valleys depends critically on the edge termination and requires atomic scale engineering of individual carbon atoms. A simulation of an equivalent optical structure shows that an optical version of a valley-polarized beam splitter might be feasible experimentally [12].The photonic crystal structure that we investigate is a triangular lattice of Al 2 O 3 ceramic rods with a lattice constant a ¼ 8 mm. The rods have a diameter of 5.1 mm and a dielectric constant ¼ 9:8 [13].…”

mentioning

confidence: 99%

“…There are two inequivalent corners or K points that are not connected by a reciprocal lattice vector, leading to two distinct K and K 0 valleys. Predictions for electrons in graphene that make use of these valleys, e.g., a valleypolarized beam splitter [12], are difficult to realize since the coupling of electron wave functions to different valleys depends critically on the edge termination and requires atomic scale engineering of individual carbon atoms. A simulation of an equivalent optical structure shows that an optical version of a valley-polarized beam splitter might be feasible experimentally [12].…”

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confidence: 99%

Experimental Observation of Strong Edge Effects on the Pseudodiffusive Transport of Light in Photonic Graphene

2010

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Photonic graphene is a two-dimensional photonic crystal structure that is analogous to graphene. We use 5 mm diameter Al 2 O 3 rods placed on a triangular lattice with a lattice constant a ¼ 8 mm to create an isolated conical singularity in the photonic band structure at a microwave frequency of 17.6 GHz. At this frequency, the measured transmission of microwaves through a perfectly ordered structure enters a pseudodiffusive regime where the transmission scales inversely with the thickness L of the crystal (L=a * 5). The transmission depends critically on the configuration of the edges: distinct oscillations with an amplitude comparable to the transmission are observed for structures terminated with zigzag edges, while these oscillations are absent for samples with a straight edge configuration. DOI: 10.1103/PhysRevLett.104.043903 PACS numbers: 42.25.Gy, 42.25.Bs, 42.70.Qs The experimental realization of graphene [1], a single layer of carbon atoms arranged in a two-dimensional hexagonal structure, has attracted a lot of attention. The interest in this gapless semiconductor is due to the conical singularities in the electronic band structure [2] that create a linear dispersion for electrons, leading to interesting physical phenomena such as an anomalous quantum Hall effect and the absence of Anderson localization [3,4]. Since the dispersion around these points is linear, the motion of electrons resembles that of massless particles and can be described by the relativistic Dirac equation. These singularities have been aptly named ''Dirac points'' and are entirely due to the geometry of the underlying triangular lattice.As a consequence, similar conical singularities can be identified in the band structure of electromagnetic waves in two-dimensional photonic crystals with a triangular lattice [5][6][7], acoustic waves in a sonic crystal [8], and electrons in a two-dimensional electron gas [9]. Of these analogous systems, only the propagation of acoustic waves was studied experimentally, and an acoustic analogue to the Zitterbewegung of relativistic electrons was identified [8]. The analogy between graphene and these structures strengthens our understanding of the physics common to these two-dimensional structures. In particular, the analogy with optics has already inspired researchers to predict known optical effects, such as negative refraction [10] and a Goos-Hänchen shift for electrons in graphene [11].Despite the success of graphene, the observation of effects predicted by theory often require samples with perfect edges of a well-defined configuration that can only be obtained by atomic scale engineering. In this Letter, we experimentally investigate a photonic crystal structure for microwave frequencies that is analogous to graphene and realize samples with ideal edges on a much more accessible millimeter length scale. The transmission at the Dirac point of this perfectly ordered structure enters a pseudodiffusive transport regime and becomes inversely proportional to the thickness of the sample, as predic...

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“…Thus far, the search for an easy-to-implement, all-electricfield-controlled valley filter remains an ongoing challenge. Beyond valley filters, valley beam splitter, operating via an electron-optics approach [44], has been explored as an alternative building block of valleytronics [45].…”

Section: Introductionmentioning

confidence: 99%

Valleytronics in merging Dirac cones: All-electric-controlled valley filter, valve, and universal reversible logic gate

et al. 2017

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Despite much anticipation of valleytronics as a candidate to replace the aging complementary metal-oxidesemiconductor (CMOS) based information processing, its progress is severely hindered by the lack of practical ways to manipulate valley polarization all electrically in an electrostatic setting. Here, we propose a class of all-electric-controlled valley filter, valve, and logic gate based on the valley-contrasting transport in a merging Dirac cones system. The central mechanism of these devices lies on the pseudospin-assisted quantum tunneling which effectively quenches the transport of one valley when its pseudospin configuration mismatches that of a gate-controlled scattering region. The valley polarization can be abruptly switched into different states and remains stable over semi-infinite gate-voltage windows. Colossal tunneling valleypseudomagnetoresistance ratio of over 10000% can be achieved in a valley-valve setup. We further propose a valleytronic-based logic gate capable of covering all 16 types of two-input Boolean logics. Remarkably, the valley degree of freedom can be harnessed to resurrect logical reversibility in two-input universal Boolean gate. The (2+1) polarization states (two distinct valleys plus a null polarization) reestablish one-to-one inputto-output mapping, a crucial requirement for logical reversibility, and significantly reduce the complexity of reversible circuits. Our results suggest that the synergy of valleytronics and digital logics may provide new paradigms for valleytronic-based information processing and reversible computing. Despite much anticipation of valleytronics as a candidate to replace the aging complementary metal-oxidesemiconductor (CMOS) based information processing, its progress is severely hindered by the lack of practical ways to manipulate valley polarization all electrically in an electrostatic setting. Here, we propose a class of all-electric-controlled valley filter, valve, and logic gate based on the valley-contrasting transport in a merging Dirac cones system. The central mechanism of these devices lies on the pseudospin-assisted quantum tunneling which effectively quenches the transport of one valley when its pseudospin configuration mismatches that of a gate-controlled scattering region. The valley polarization can be abruptly switched into different states and remains stable over semi-infinite gate-voltage windows. Colossal tunneling valley-pseudomagnetoresistance ratio of over 10 000% can be achieved in a valley-valve setup. We further propose a valleytronic-based logic gate capable of covering all 16 types of two-input Boolean logics. Remarkably, the valley degree of freedom can be harnessed to resurrect logical reversibility in two-input universal Boolean gate. The (2 + 1) polarization states (two distinct valleys plus a null polarization) reestablish one-to-one input-to-output mapping, a crucial requirement for logical reversibility, and significantly reduce the complexity of reversible circuits. Our results suggest that the synergy of va...

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Fully Valley-Polarized Electron Beams in Graphene

Cited by 231 publications

References 21 publications

Helical scattering and valleytronics in bilayer graphene

Helical scattering and valleytronics in bilayer graphene

Experimental Observation of Strong Edge Effects on the Pseudodiffusive Transport of Light in Photonic Graphene

Valleytronics in merging Dirac cones: All-electric-controlled valley filter, valve, and universal reversible logic gate

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