A valley-filtering switch based on strained graphene

Zhai, Feng; Ma, Yanling; Zhang, Ying-Tao

doi:10.1088/0953-8984/23/38/385302

Cited by 36 publications

(29 citation statements)

References 37 publications

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“…Their interpretation proposes that the formation of bulk topological valley currents is intertwined with the presence of a Berry curvature generated by the mass term [23], a scenario which is under questioning [24,25]. Accordingly to date, despite the wealth of theoretical proposals of valley dependent effects [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], experimental fingerprints of PMF on quantum transport and unambiguous demonstration of a valley Hall effect in graphene remain elusive.Here, we predict that once the electronic structure of Dirac fermions embeds a strain-related gauge field, it is possible to fine-tune the superposition of an external real magnetic field to reach a resonant effect, where the sum of valley-dependent effective magnetic fields either sum up or cancel each other. This results in a remarkable valley-polarized quantum transarXiv:1705.09085v2 [cond-mat.mes-hall] 1 Jul 2017…”

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confidence: 99%

Valley-polarized quantum transport generated by gauge fields in graphene

2017

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We report on the possibility to simultaneously generate in gaphene a bulk valley-polarized dissipative transport and a quantum valley Hall effect by combining strain-induced gauge fields and real magnetic fields. Such unique phenomenon results from a "resonance/anti-resonance" effect driven by the superposition/cancellation of superimposed gauge fields which differently affect time reversal symmetry. The onset of a valley-polarized Hall current concomitant to a dissipative valley-polarized current flow in the opposite valley is revealed by a e 2 /h Hall conductivity plateau. We employ efficient linear scaling Kubo transport methods combined with a valley projection scheme to access valley-dependent conductivities and show that the results are robust against disorder.In graphene and other two-dimensional materials, degenerate valleys of energy bands, well-separated in momentum space, constitute a discrete degree of freedom for low-energy carriers, provided intervalley mixing is negligible (case of long range disorder). Such valley degree of freedom can then be seen as a nonvolatile information carrier, provided that it can be coupled to external probes. Similarly to research in graphene spintronics [1,2], valleytronics and controlling the valley degree of freedom in graphene and other 2D materials has attracted a considerable attention [3][4][5], and many studies have investigated different options to realize valley polarized current or to filter electrons with a given valley polarization [6][7][8][9][10][11][12]. In presence of broken inversion symmetry, the valley index is also predicted to play a similar role as the spin degree of freedom in phenomena such as Hall transport, magnetization, optical transition selection rules, and chiral edge modes [13][14][15][16]. Recently, it has been shown that for modest levels of strain, graphene can also sustain a classical valley Hall effect that can be detected in nonlocal transport measurements [17]. All this stimulates the search for efficient control of valley dynamics by magnetic, electric, and optical means, which would form the basis of valley based information processing.On the other hand, it was soon realized that nonuniformly strained graphene can be modeled by the inclusion of a gauge field in the effective Hamiltonian (though it is not Berry-like). Such gauge field preserves time reversal symmetry, but induces pseudomagnetic fields (PMFs) of opposite signs in the two valleys forming the low-energy electronic bandstructure [18]. In particular, mechanical deformations aligned along three main crystallographic directions were predicted to generate strong gauge fields, acting effectively as an uniform magnetic field, opening the possibility to trigger a pseudomagnetic quantum Hall effect for strained superlattices [19]. Experimentally, evidences of PMFs with values varying from few tens up to hundreds of Tesla have been reported [20,21]. Finally, Gorbachev and coworkers recently measured intriguingly large nonlocal resistance signals in a situation where the alig...

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confidence: 99%

Valley-polarized quantum transport generated by gauge fields in graphene

2017

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“…26 The appearance of valley polarized currents is necessary for valleytronic applications. Several valley filtering schemes for graphene have been proposed, 21,23,24,[27][28][29][30][31] by making use of graphene nanoconstrictions, 21 valley-dependent trigonal warping of the carrier dispersion, 23,24 line defects, 27 applying magnetic fields to the strained graphene, [28][29][30] and applying magnetic-electric barriers to graphene with a Dirac gap. 31 In this work, we propose a valley filter based on the uniaxially strained bulk graphene irradiated by linearly polarized light.…”

Section: Mechanically and Optically Controlled Graphene Valley Filtermentioning

confidence: 99%

Mechanically and optically controlled graphene valley filter

Jin

2014

Journal of Applied Physics

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We theoretically investigate the valley-dependent electronic transport through a graphene monolayer modulated simultaneously by a uniform uniaxial strain and linearly polarized light. Within the Floquet formalism, we calculate the transmission probabilities and conductances of the two valleys. It is found that valley polarization can appear only if the two modulations coexist. Under a proper stretching of the sample, the ratio of the light intensity and the light frequency squared is important. If this quantity is small, the electron transport is mainly contributed by the valley-symmetric central band and the conductance is valley unpolarized; but when this quantity is large, the valley-asymmetric sidebands also take part in the transport and the valley polarization of the conductance appears. Furthermore, the degree of the polarization can be tuned by the strain strength, light intensity, and light frequency. It is proposed that the detection of the valley polarization can be realized utilizing the valley beam splitting. Thus, a graphene monolayer can be used as a mechanically and optically controlled valley filter.

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“…where ϕ L11 , ϕ L12 (ϕ R11 , ϕ R12 ) are the phase factors of the left (right) barrier given by Eqs. (16) and (18). Because of the phase factor φ τ resonant transmission peaks will occur when,…”

Section: Barrier Structurementioning

confidence: 99%

Resonant valley filtering of massive Dirac electrons

et al. 2012

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Electrons in graphene, in addition to their spin, have two pseudospin degrees of freedom: sublattice and valley pseudospin. Valleytronics uses the valley degree of freedom as a carrier of information similar to the way spintronics uses electron spin. We show how a double barrier structure consisting of electric and vector potentials can be used to filter massive Dirac electrons based on their valley index. We study the resonant transmission through a finite number of barriers and we obtain the energy spectrum of a superlattice consisting of electric and vector potentials. When a mass term is included the energy bands and energy gaps at the K and K' points are different and they can be tuned by changing the potential.Comment: 20 figure

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A valley-filtering switch based on strained graphene

Cited by 36 publications

References 37 publications

Valley-polarized quantum transport generated by gauge fields in graphene

Valley-polarized quantum transport generated by gauge fields in graphene

Mechanically and optically controlled graphene valley filter

Resonant valley filtering of massive Dirac electrons

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