Effective tight-binding model for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>M</mml:mi><mml:msub><mml:mi>X</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>under electric and magnetic fields

Shanavas, K. V.; Satpathy, S.

doi:10.1103/physrevb.91.235145

Cited by 35 publications

(32 citation statements)

References 31 publications

(27 reference statements)

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“…This would introduce a splitting at Γ , which we do not observe 26,27 . Furthermore, we can rule out any potassium-induced structural symmetry breaking in our heterostructure, as only minor rigid binding-energy shifts of the S 2p core levels of WS 2 and of the underlying h-BN π-band are observed after complete doping (see Supplementary Figs.…”

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confidence: 99%

Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

et al. 2018

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In two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), new electronic phenomena such as tunable bandgaps 1-3 and strongly bound excitons and trions emerge from strong many-body effects [4][5][6] , beyond the spin and valley degrees of freedom induced by spin-orbit coupling and by lattice symmetry 7 . Combining single-layer TMDs with other 2D materials in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these many-body effects, by means of engineered interlayer interactions [8][9][10] . Here, we use micro-focused angle-resolved photoemission spectroscopy (microARPES) and in situ surface doping to manipulate the electronic structure of single-layer WS 2 on hexagonal boron nitride (WS 2 /h-BN). Upon electron doping, we observe an unexpected giant renormalization of the spin-orbit splitting of the single-layer WS 2 valence band, from 430 meV to 660 meV, together with a bandgap reduction of at least 325 meV, attributed to the formation of trionic quasiparticles. These findings suggest that the electronic, spintronic and excitonic properties are widely tunable in 2D TMD/h-BN heterostructures, as these are intimately linked to the quasiparticle dynamics of the materials [11][12][13] . Coulomb interactions in 2D materials are several times stronger than in their 3D counterparts. In 2D TMDs, this is most directly evidenced by the presence of excitons with binding energies an order of magnitude higher than in the bulk 4 . Although the excitons in these 2D materials have been widely studied by optical techniques 13 , the impact of strong electron-electron interactions on the quasiparticle band structure remains unclear. Theory predicts that many-body effects will influence the spin-orbit splitting around the valenceband maximum (VBM) and conduction-band minimum (CBM) 14 . Although these should be observable by ARPES, a direct probe of many-body effects 15 , measurements so far have mainly focused on the layer-dependence of the single-particle spectrum and the direct bandgap transition in 2D TMD systems, including epitaxial single- . Unfortunately, the lateral size of mechanically assembled heterostructures is usually of the order of 10 μ m, much smaller than the beam spot of typical ARPES setups (≳ 100 μ m). Furthermore, sample charging on insulating bulk h-BN substrates would complicate ARPES experiments.We overcome these challenges as follows. We realize a high-quality 2D semiconductor-insulator interface by mechanically transferring a relatively large (~100 μ m) single-layer WS 2 crystal onto a thin flake of h-BN that has itself been transferred onto a degenerately doped TiO 2 substrate, as depicted in Fig. 1a. Sample charging is avoided because there is electrical contact from the continuous single-layer WS 2 flake to both the h-BN and the conductive TiO 2 . Figure 1b is an optical microscope image of the sample, including a flake of h-BN, approximately 100 μ m wide, surrounded by several transferred flakes of single-layer WS 2 on the Ti...

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Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

et al. 2018

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“…In spin-space, the standard spin-orbit matrix element for d orbital was used. 34 The effect of vertical electric field was introduced by the on-site potential difference U between the bilayers.…”

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“…Then, the initial 7 × 7 Hamiltonian can be reduced to 5 × 5 effective Hamiltonian through Löwdin down-folding. 34 To consider the effect of spin-orbit coupling and interlayer coupling, the monolayer Hamiltonian was expanded to the 20 × 20 matrix in spin and layer pseudo-spin space.…”

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Universal Mechanism of Band-Gap Engineering in Transition-Metal Dichalcogenides

et al. 2017

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van der Waals two-dimensional (2D) semiconductors have emerged as a class of materials with promising device characteristics owing to the intrinsic band gap. For realistic applications, the ideal is to modify the band gap in a controlled manner by a mechanism that can be generally applied to this class of materials. Here, we report the observation of a universally tunable band gap in the family of bulk 2H transition metal dichalcogenides (TMDs) by in situ surface doping of Rb atoms. A series of angle-resolved photoemission spectra unexceptionally shows that the band gap of TMDs at the zone corners is modulated in the range of 0.8–2.0 eV, which covers a wide spectral range from visible to near-infrared, with a tendency from indirect to direct band gap. A key clue to understanding the mechanism of this band-gap engineering is provided by the spectroscopic signature of symmetry breaking and resultant spin-splitting, which can be explained by the formation of 2D electric dipole layers within the surface bilayer of TMDs. Our results establish the surface Stark effect as a universal mechanism of band-gap engineering on the basis of the strong 2D nature of van der Waals semiconductors.

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“…In fact, the Rashba SOC is automatically excluded from the model. With the coupling being proportional to the matrix element of z [41] between states, it vanishes between any pair of states from…”

Section: B Tmdc-based Quantum Structuresmentioning

confidence: 99%

Electrical valley filtering in transition metal dichalcogenides

Hsieh

Chou

2018

Phys. Rev. Materials

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This work investigates the feasibility of electrical valley filtering for holes in transition metal dichalcogenides. We look specifically into the scheme that utilizes a potential barrier to produce valleydependent tunneling rates, and perform the study with both a kp  based analytic method and a recursive Green's function based numerical method. The study yields the transmission coefficient as a function of incident energy and transverse wave vector, for holes going through lateral quantum barriers oriented in either armchair or zigzag directions, in both homogeneous and heterogeneous systems. The main findings are the following: 1) the tunneling current valley polarization increases with increasing barrier width or height, 2) both the valley-orbit interaction and band structure warping contribute to valley-dependent tunneling, with the former contribution being manifest in structures with asymmetric potential barriers, and the latter being orientation-dependent and reaching maximum for transmission in the armchair direction, and 3) for transmission ~ 0.1, a tunneling current valley polarization of the order of 10% can be achieved.

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Effective tight-binding model forMX2under electric and magnetic fields

Cited by 35 publications

References 31 publications

Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

Giant spin-splitting and gap renormalization driven by trions in single-layer WS2/h-BN heterostructures

Universal Mechanism of Band-Gap Engineering in Transition-Metal Dichalcogenides

Electrical valley filtering in transition metal dichalcogenides

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