Quantized Transport, Strain-Induced Perfectly Conducting Modes, and Valley Filtering on Shape-Optimized Graphene Corbino Devices

Jones, Gareth Wyn; Bahamon, D. A.; Neto, A. H. Castro; Pereira, Vitor M.

doi:10.1021/acs.nanolett.7b01663

Cited by 34 publications

(27 citation statements)

References 45 publications

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“…These edge states can represent snake-like trajectories 40 at the interfaces between zones of opposite pseudo-magnetic fields [41][42][43] . Since the direction of these magnetic fields is valley dependent [16][17][18] , our graphene ripples can also be a potential candidate for exploring valley dependent transport phenomena 9,41,44 . In our measurements, the spectral signatures of the snake states are seen in an increased intensity of the LDOS peaks at the ripple crests and troughs (Fig.…”

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confidence: 99%

Strain Modulated Superlattices in Graphene

et al. 2020

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Strain engineering of graphene takes advantage of one of the most dramatic responses of Dirac electrons enabling their manipulation via strain-induced pseudo-magnetic fields. Numerous theoretically proposed devices, such as resonant cavities and valley filters, as well as novel phenomena, such as snake states, could potentially be enabled via this effect. These proposals, however, require strong, spatially oscillating magnetic fields while to date only the generation and effects of pseudo-gauge fields which vary at a length scale much larger than the magnetic length have been reported. Here we create a periodic pseudo-gauge field profile using periodic strain that varies at the length scale comparable to the magnetic length and study its effects on Dirac electrons. A periodic strain profile is achieved by pulling on graphene with extreme (>10%) strain and forming nanoscale ripples, akin to a plastic wrap pulled taut at its edges. Combining scanning tunneling microscopy and atomistic calculations, we find that spatially oscillating strain results in a new quantization different from the familiar Landau quantization observed in previous studies. We also find that graphene ripples are characterized by large variations in carbon-carbon bond length, directly impacting the electronic coupling between atoms, which within a single ripple can be as different as in two different materials. The result is a single graphene sheet that effectively acts as an electronic superlattice. Our results thus also establish a novel approach to synthesize an effective 2D lateral heterostructure -by periodic modulation of lattice strain. Main Text:Due to its high electronic mobility, optical transparency, mechanical strength and flexibility, graphene is attractive for electronic applications 1,2 . However, several factors prevent the realization of common electronic applications. For example, the lack of a band gap prevents an effective off-state in graphene transistors. Furthermore, Klein tunneling 3 , in which electrons pass through an electrostatic barrier with perfect transmission, prevents electron confinement by traditional gating methods. Figure 1. Engineering periodic pseudo electric and magnetic fields at strained interfaces: (a)High(low) density of carbon atoms and hence electrons are created in regions marked by lightblue (yellow) regions due to a strain gradient. This inhomogeneous charge distribution results in an electric field (green arrows). (b) Stretching of bonds cause the Dirac cones at K and K' points to shift symmetrically (yellow) from their original unstrained positions (light-blue) in the reciprocal space. As a momentum shift can be interpreted as generating a pseudo-vector potential term eA/c 15 , (where is the electronic charge and is the velocity of light) this creates pseudo-magnetic fields with opposite signs at the two valleys. (c) The strain associated with rippling creates rare (yellow) and dense (turquoise) regions in the graphene, effectively acting as two different materials in a superlattice. (d) Pseudo...

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Strain Modulated Superlattices in Graphene

et al. 2020

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“…Moreover, its interpolating form has the ability to focus the electron beams. The different valley polariza- 3 Only two of these valleys are inequivalent, but for clarity we prefer to draw all six of them. The numerical exact agreement of the projections in equivalent valleys provides also a consistency check of our computer code.…”

Section: A Current Flow In Flat and Deformed Graphene Nanoribbonsmentioning

confidence: 99%

Current splitting and valley polarization in elastically deformed graphene

Stegmann¹,

Szpak²

2018

2D Mater.

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Elastic deformations of graphene can significantly change the flow paths and valley polarization of the electric currents. We investigate these phenomena in graphene nanoribbons with localized outof-plane deformations by means of tight-binding transport calculations. Such deformations can split the current into two beams of almost completely valley polarized electrons and give rise to a valley voltage. These properties are observed for a fairly wide set of experimentally accessible parameters. We propose a valleytronic nanodevice in which a high polarization of the electrons comes along with a high transmission making the device very efficient. In order to gain a better understanding of these effects, we also treat the system in the continuum limit in which the electronic excitations can be described by the Dirac equation coupled to curvature and a pseudo-magnetic field. Semiclassical trajectories offer then an additional insight into the balance of forces acting on the electrons and provide a convenient tool for predicting the behavior of the current flow paths. The proposed device can also be used for a sensitive measurement of graphene deformations. arXiv:1806.09576v2 [cond-mat.mes-hall]

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“…Middle column shows the field profile calculated from the deformation field shown in the right column. Recently, those authors and co-workers used the same technique to optimize a graphene Corbino device for valley filltering applications [27].…”

Section: Strain Engineeringmentioning

confidence: 99%

Strained Graphene Structures: From Valleytronics to Pressure Sensing

Milovanović

Peeters

2018

NATO Science for Peace and Security Series A: Chemistry and Biology

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Due to its strong bonds graphene can stretch up to 25% of its original size without breaking. Furthermore, mechanical deformations lead to the generation of pseudo-magnetic fields (PMF) that can exceed 300 T. The generated PMF has opposite direction for electrons originating from different valleys. We show that valley-polarized currents can be generated by local straining of multi-terminal graphene devices. The pseudo-magnetic field created by a Gaussian-like deformation allows electrons from only one valley to transmit and a current of electrons from a single valley is generated at the opposite side of the locally strained region. Furthermore, applying a pressure difference between the two sides of a graphene membrane causes it to bend/bulge resulting in a resistance change. We find that the resistance changes linearly with pressure for bubbles of small radius while the response becomes non-linear for bubbles that stretch almost to the edges of the sample. This is explained as due to the strong interference of propagating electronic modes inside the bubble. Our calculations show that high gauge factors can be obtained in this way which makes graphene a good candidate for pressure sensing. arXiv:1711.07904v1 [cond-mat.mes-hall]

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Quantized Transport, Strain-Induced Perfectly Conducting Modes, and Valley Filtering on Shape-Optimized Graphene Corbino Devices

Cited by 34 publications

References 45 publications

Strain Modulated Superlattices in Graphene

Strain Modulated Superlattices in Graphene

Current splitting and valley polarization in elastically deformed graphene

Strained Graphene Structures: From Valleytronics to Pressure Sensing

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