Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures

Wallbank, John; Ghazaryan, Davit; Misra, Abhishek; Cao, Yun; Tu, J. S.; Piot, B. A.; Potemski, M.; Pezzini, Sergio; Wiedmann, Steffen; Zeitler, U.; Lane, Thomas; Морозов, С. В.; Greenaway, M. T.; Eaves, L.; Geǐm, A. K.; Fal’ko, Vladimir I.; Новоселов, К. С.; Mishchenko, Artem

doi:10.1126/science.aaf4621

Cited by 90 publications

(74 citation statements)

References 52 publications

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“…Resonate tunneling current and negative differential resistance (NDR) have been observed in graphene‐based heterostructure TFETs, including monolayer and bilayer graphene separated by BN25, 26, 27, 28, 29, 30 or TMDs 6, 31. However, due to the absence of a bandgap, graphene‐based TFETs are unable to obtain a high on/off ratio of the current.…”

Section: Introductionmentioning

confidence: 99%

Independent Band Modulation in 2D van der Waals Heterostructures via a Novel Device Architecture

et al. 2018

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Benefiting from the technique of vertically stacking 2D layered materials (2DLMs), an advanced novel device architecture based on a top‐gated MoS2/WSe2 van der Waals (vdWs) heterostructure is designed. By adopting a self‐aligned metal screening layer (Pd) to the WSe2 channel, a fixed p‐doped state of the WSe2 as well as an independent doping control of the MoS2 channel can be achieved, thus guaranteeing an effective energy‐band offset modulation and large through current. In such a device, under specific top‐gate voltages, a sharp PN junction forms at the edge of the Pd layer and can be effectively manipulated. By varying top‐gate voltages, the device can be operated under both quasi‐Esaki diode and unipolar‐Zener diode modes with tunable current modulations. A maximum gate‐coupling efficiency as high as ≈90% and a subthreshold swing smaller than 60 mV dec−1 can be achieved under the band‐to‐band tunneling regime. The superiority of the proposed device architecture is also confirmed by comparison with a traditional heterostructure device. This work demonstrates the feasibility of a new device structure based on vdWs heterostructures and its potential in future low‐power electronic and optoelectronic device applications.

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Section: Introductionmentioning

confidence: 99%

Independent Band Modulation in 2D van der Waals Heterostructures via a Novel Device Architecture

et al. 2018

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“…1b. In previously studied devices with hBN barriers, the passage of the Fermi level through the zero in the density of states at the Dirac points of the top and bottom graphene electrodes is observed as an X-shaped feature in the colour map 10,11,19,25 , where G=0. This feature is not observed in the devices with a CrBr 3 barrier.…”

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confidence: 95%

Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr3

et al. 2018

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The growing family of two-dimensional (2D) materials 1-3 can be used to assemble van der Waals heterostructures with a wide range of properties 4-6 . Of particular interest are tunnelling heterostructures 7-9 , which have been used to study the electronic states both in the tunnelling barrier and in the emitter and collector contacts 10,11 . Recently, 2D ferromagnets have been studied theoretically 12-15 and experimentally 16-18 . Here we investigate electron tunnelling through a thin (2-6 layers) ferromagnetic CrBr 3 barrier. For devices with non-magnetic barriers, conservation of momentum can be relaxed by phonon-assisted tunnelling 8,19-21 or by tunnelling through localised states 8,21,22 . In the case of our ferromagnetic barrier the dominant tunnelling mechanisms are the emission of magnons 18 at low temperatures or scattering of electrons on localised magnetic excitations above the Curie temperature. Magnetoresistance in the graphene electrodes further suggests induced spin-orbit coupling and proximity exchange via the ferromagnetic barrier. Tunnelling with magnon emission offers the possibility of spin-injection, as has been previously demonstrated with other ferromagnetic barriers 23,24 . S1. Device fabrication S2. Temperature dependence of differential dI/dV b conductance on magnetic field for devices with different thickness of CrBr 3 S3. Quantum capacitance of Gr/CrBr 3 /Gr devices S4. Calculation of magnon density of states S5. Scattering rates

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“…This provides a new opportunity in device design where electronic properties are controlled by varying the relative twist angle between layers [1]. Indeed several studies have established that in heterostructures assembled from 2D crystals, electron tunneling between layers varies strongly with rotation [2][3][4][5][6][7][8]. In twisted bilayer graphene (two monolayers in direct contact but with an angle mismatch between the layers) several novel phenomenon have been predicted and observed, including topological valley transport [9][10][11][12][13], and superconductivity [14], as a consequence of angledependent interlayer coupling.…”

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confidence: 99%

Twistable electronics with dynamically rotatable heterostructures

Ribeiro-Palau

Zhang

Watanabe

et al. 2018

Science

454

361

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The electronic properties of two-dimensional materials and their heterostructures can be dramatically altered by varying the relative angle between the layers. This makes it theoretically possible to realize a new class of twistable electronics in which device properties can be manipulated on-demand by simply rotating the structure. Here, we demonstrate a new device architecture in which a layered heterostructure can be dynamically twisted, in situ. We study graphene encapsulated by boron nitride where at small rotation angles the device characteristics are dominated by coupling to a large wavelength Moiré superlattice. The ability to investigate arbitrary rotation angle in a single device reveals new features in the optical, mechanical and electronic response in this system. Our results establish the capability to fabricate twistable electronic devices with dynamically tunable properties.The weak van der Walls forces between the atomic planes in 2D materials makes it possible to fabricate devices with arbitrary rotational order. This provides a new opportunity in device design where electronic properties are controlled by varying the relative twist angle between layers [1]. Indeed several studies have established that in heterostructures assembled from 2D crystals, electron tunneling between layers varies strongly with rotation [2][3][4][5][6][7][8]. In twisted bilayer graphene (two monolayers in direct contact but with an angle mismatch between the layers) several novel phenomenon have been predicted and observed, including topological valley transport [9-13], and superconductivity [14], as a consequence of angledependent interlayer coupling. Likewise, the formation of interlayer excitons in transition metal dichalcogenide heterostructures is highly sensitive to angle [15][16][17].The effect of rotational alignment between conducting and insulating 2D layers can be equally significant. A remarkable example is provided by graphene coupled to hexagonal boron nitride (BN). Owing to the closely matched lattice constants a large Moiré superlattice develops near zero angle mismatch [18,19]. This substantially alters the graphene band structure opening an energy gap at the charge neutrality point (CNP) and creating replica Dirac points at higher energies [20][21][22].Several techniques have been developed to fabricate layered heterostructures with controlled rotation between the layers, including optical alignment of crystal edges [18,[20][21][22], rotational alignment [23] during assembly, and self-alignment through thermal annealing [24,25]). However, in each case a priori understanding of the crystallographic orientation of each layer is required before assembly; motion between the layers during assembly makes it difficult to achieve precise angle control; and most significantly, once assembled the angle can not be further modified. Here, we present a new experimental technique that provides on-demand control of the orientation between layers in a van der Waals heterostructure. We study a BN/graphene/BN structure w...

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Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures

Cited by 90 publications

References 52 publications

Independent Band Modulation in 2D van der Waals Heterostructures via a Novel Device Architecture

Independent Band Modulation in 2D van der Waals Heterostructures via a Novel Device Architecture

Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr3

Twistable electronics with dynamically rotatable heterostructures

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