Valley filtering using electrostatic potentials in bilayer graphene

Costa, D. R. da; Chaves, Andrey; Sena, S. H. R.; Farias, G. A.; Peeters, F. M.

doi:10.1103/physrevb.92.045417

Cited by 48 publications

(57 citation statements)

References 25 publications

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“…Valley filters, serving as valley polarized current generator and allowing only carriers of a specific valley passing through, are one important type of valleytronics devices [21]. Theoretical researches predicted that kink states in the line defect of few layer graphene host the transmission of valley polarized current [22][23][24][25][26][27][28][29][30]. In a hexagonal lattice, when the effective mass of carriers changes its sign across the line defect, the kink states are formed along the line defect with zero mass.…”

Section: Introductionmentioning

confidence: 99%

The valley filter efficiency of monolayer graphene and bilayer graphene line defect model

et al. 2016

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Figure 3. The performance of model I in the presence of disorder. The results for Anderson (long range) disorder is exhibited in a1-f1 (a2-f2). The other parameters are d=20 and M=100. AbstractIn addition to electron charge and spin, novel materials host another degree of freedom, the valley. For a junction composed of valley filter sandwiched by two normal terminals, we focus on the valley efficiency under disorder with two valley filter models based on monolayer and bilayer graphene. Applying the transfer matrix method, valley resolved transmission coefficients are obtained. We find that: (i) under weak disorder, when the line defect length is over about 15 nm, it functions as a perfect channel (quantized conductance) and valley filter (totally polarized); (ii) in the diffusive regime, combination effects of backscattering and bulk states assisted intervalley transmission enhance the conductance and suppress the valley polarization; (iii) for very long line defect, though the conductance is small, polarization is indifferent to length. Under perpendicular magnetics field, the characters of charge and valley transport are only slightly affected. Finally we discuss the efficiency of transport valley polarized current in a hybrid system.

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Section: Introductionmentioning

confidence: 99%

The valley filter efficiency of monolayer graphene and bilayer graphene line defect model

et al. 2016

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“…Different routes have been suggested to create valley polarization in graphene [13][14][15][16][17], relying on nanoribbons or constrictions [17][18][19][20][21], interplays between external fields [22][23][24][25], spin-orbit coupling [26,27], or spatial or temporal combinations of gating and magnetic fields [28][29][30]. However, an experimental verification has proven to be challenging as practical and effective methods to manipulate the valleys in realistic setups still need to be established.…”

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Graphene Nanobubbles as Valley Filters and Beam Splitters

et al. 2016

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The low energy band structure of graphene has two inequivalent valleys at K and K points of the Brillouin zone. The possibility to manipulate this valley degree of freedom defines the field of valleytronics, the valley analogue of spintronics. A key requirement for valleytronic devices is the ability to break the valley degeneracy by filtering and spatially splitting valleys to generate valley polarized currents. Here we suggest a way to obtain valley polarization using strain-induced inhomogeneous pseudomagnetic fields (PMF) which act differently on the two valleys. Notably, the suggested method does not involve external magnetic fields, or magnetic materials, as in previous proposals. In our proposal the strain is due to experimentally feasible nanobubbles, whose associated PMFs lead to different real space trajectories for K and K electrons, thus allowing the two valleys to be addressed individually. In this way, graphene nanobubbles can be exploited in both valley filtering and valley splitting devices, and our simulations reveal that a number of different functionalities are possible depending on the deformation field.

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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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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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Valley filtering using electrostatic potentials in bilayer graphene

Cited by 48 publications

References 25 publications

The valley filter efficiency of monolayer graphene and bilayer graphene line defect model

The valley filter efficiency of monolayer graphene and bilayer graphene line defect model

Graphene Nanobubbles as Valley Filters and Beam Splitters

Valley-polarized quantum transport generated by gauge fields in graphene

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