Strongly Enhanced Tunneling at Total Charge Neutrality in Double-Bilayer Graphene-WSe_{2} Heterostructures (original) (raw)
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Nano letters, 2017
We demonstrate gate-tunable resonant tunneling and negative differential resistance between two rotationally aligned bilayer graphene sheets separated by bilayer WSe2. We observe large interlayer current densities of 2 and 2.5 μA/μm(2) and peak-to-valley ratios approaching 4 and 6 at room temperature and 1.5 K, respectively, values that are comparable to epitaxially grown resonant tunneling heterostructures. An excellent agreement between theoretical calculations using a Lorentzian spectral function for the two-dimensional (2D) quasiparticle states, and the experimental data indicates that the interlayer current stems primarily from energy and in-plane momentum conserving 2D-2D tunneling, with minimal contributions from inelastic or non-momentum-conserving tunneling. We demonstrate narrow tunneling resonances with intrinsic half-widths of 4 and 6 meV at 1.5 and 300 K, respectively.
Effect of interlayer bare tunneling on electron-hole coherence in graphene bilayers
Physical Review B, 2011
The influence of single-particle interlayer coupling on the many-body electron-hole condensation between two graphene monolayers separated by a thin dielectric film is studied. This work extends prior work by treating interlayer coupling, which controls critical interlayer tunneling currents, nonperturbatively. As before, a π-band tight-binding model of the graphene bilayer is combined with Fock mean-field theory. Our results demonstrate that both the strength and the sublattice distribution of interlayer coupling play essential roles. We consider both Bernal-like and quasi-hexagonal forms, and self-consistently solve for the condensate. We find that stronger bare coupling can considerably affect the nature of the condensate state itself, selecting a preferred pattern of interlayer coherence among the atomic sublattices. When this occurs, the sensitivity of the critical current to the nature of the bare coupling decreases substantially. Because condensate control via gated charge imbalance has been proposed for beyond Complementary Metal-Oxide Semiconductor (CMOS) switching, we also examine the effect of increasing charge imbalance between layers on the condensate strength as well as the critical current.
Band Tunneling through Double Barrier in Bilayer Graphene
By taking into account the full four band energy spectrum, we calculate the transmission probability and conductance of electrons across symmetric and asymmetric double potential barrier with a confined interlayer potential difference in bilayer graphene. For energies less than the interlayer coupling γ1, E < γ1, we have one channel for transmission which exhibits resonances, even for incident particles with energies less than the strength of barriers, E < Uj, depending on the double barrier geometry. In contrast, for higher energies E > γ1, we obtain four possible ways for transmission resulting from the two propagating modes. We compute the associated transmission probabilities as well as their contribution to the conductance, study the effect of the double barrier geometry.
A Study of Vertical Transport through Graphene toward Control of Quantum Tunneling
Nano Letters, 2018
Vertical integration of van der Waals (vdW) materials with atomic precision is an intriguing possibility brought forward by these two-dimensional (2D) materials. Essential to the design and analysis of these structures is a fundamental understanding of the vertical transport of charge carriers into and across vdW materials, yet little has been done in this area. In this report, we explore the important roles of single layer graphene in the vertical tunneling process as a tunneling barrier. Although a semimetal in the lateral lattice plane, graphene together with the vdW gap act as a tunneling barrier that is nearly transparent to the vertically tunneling electrons due to its atomic thickness and the transverse momenta mismatch between the injected electrons and the graphene band structure. This is accentuated using electron tunneling spectroscopy (ETS) showing a lack of features corresponding to the Dirac cone band structure. Meanwhile, the graphene acts as a lateral conductor through which the potential and charge distribution across the tunneling barrier can be tuned. These unique properties make graphene an excellent 2D atomic grid, transparent to charge carriers, and yet can control the carrier flux via the electrical potential. A new model on the quantum capacitance's effect on vertical tunneling is developed to further elucidate the role of graphene in modulating the tunneling process. This work may serve as a general guideline for the design and analysis of vdW vertical tunneling devices and heterostructures, as well as the study of electron/spin injection through and into vdW materials.
Tunneling Plasmonics in Bilayer Graphene
Nano letters, 2015
We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At subnanometer separation, such layers can form either a strongly coupled bilayer graphene with a Bernal stacking or a weakly coupled double-layer graphene with a random stacking order. Effects due to interlayer tunneling dominate in the former case but are negligible in the latter. We found through infrared nanoimaging that bilayer graphene supports plasmons with a higher degree of confinement compared to single- and double-layer graphene, a direct consequence of interlayer tunneling. Moreover, we were able to shut off plasmons in bilayer graphene through gating within a wide voltage range. Theoretical modeling indicates that such a plasmon-off region is directly linked to a gapped insulating state of bilayer graphene, yet another implication of interlayer tunneling. Our work uncovers essential plasmonic properties in bilayer graphene and suggests a possibility to ach...
A Study of Vertical Transport through Graphene towards Control of Quantum Tunneling
Nano letters, 2018
Vertical integration of van der Waals (vdW) materials with atomic precision is an intriguing possibility brought forward by these 2-dimensional materials. Essential to the design and analysis of these structures is a fundamental understanding of the vertical transport of charge carriers into and across vdW materials, yet little has been done in this area. In this report, we explore the important roles of single layer graphene in the vertical tunneling process as a tunneling barrier. Although a semi-metal in the lateral lattice plane, graphene together with the vdW gap act as a tunneling barrier that is nearly transparent to the vertically tunneling electrons due to its atomic thickness and the transverse momenta mismatch between the injected electrons and the graphene band structure. This is accentuated using electron tunneling spectroscopy (ETS) showing a lack of features corresponding to the Dirac cone band structure. Meanwhile, the graphene acts as a lateral conductor through whi...
Quantum transport across van der Waals domain walls in bilayer graphene
Journal of Physics: Condensed Matter
Bilayer graphene can exhibit deformations such that the two graphene sheets are locally detached from each other resulting in a structure consisting of domains with different inter-layer coupling. Here we investigate how the presence of these domains affect the transport properties of bilayer graphene. We derive analytical expressions for the transmission probability, and the corresponding conductance, across walls separating different inter-layer coupling domain. We find that the transmission can exhibit a valley-dependent layer asymmetry and that the domain walls have a considerable effect on the chiral tunnelling properties of the charge carriers. We show that transport measurements allow one to obtain the strength with which the two layers are coupled. We performed numerical calculations for systems with two domain walls and find that the availability of multiple transport channels in bilayer graphene modifies significantly the conductance dependence on inter-layer potential asymmetry.
Quantum Tunneling Mechanisms in Monolayer Graphene Modulated by Multiple Electrostatic Barriers
The transmission coefficient and electronic conductance of a graphene monolayer in the presence of multi-electrostatic barriers are theoretically investigated using the transfer matrix method (TMM). The transmission coefficient, conductance, and Fano factor are evaluated as a function of the number and width of the barriers, angle/energy of incidence, as well as the applied potential at each barrier. We find that the transmission coefficient presents a series of resonances that depends on the number and widths of the barriers. Furthermore, we show that the resonant states can be suppressed for larger incidence angles and barrier widths and tuned towards lower energies. Consequently, the proposed structure can be used to fabricate new optoelectronic devices based on (ON/OFF) states as tunable field-effect transistors.
Quantum Tunneling Characteristics in Monolayer Graphene Modulated by Multiple Electrostatic Barriers
The transmission coefficient and electronic conductance of a graphene monolayer in the presence of multi-electrostatic barriers are theoretically investigated using the transfer matrix method (TMM). The transmission coefficient, conductance, and Fano factor are evaluated as a function of the number and width of the barriers, angle/energy of incidence, as well as the applied potential at each barrier. We find that the transmission coefficient presents a series of resonances that depends on the number and widths of the barriers. Furthermore, we show that the resonant states can be suppressed for larger incidence angles and barrier widths and tuned towards lower energies. Consequently, the proposed structure can be used to fabricate new optoelectronic devices based on (ON/OFF) states as tunable field-effect transistors.