Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides

Zeng, Hualing; Liu, Gui-Bin; Dai, Junfeng; Yan, Y. J.; Zhu, Bairen; He, Ruicong; Xie, Lu; Xu, Shijie; Chen, Xianhui; Yao, Wang; Cui, Xiaodong

doi:10.1038/srep01608

Cited by 956 publications

(1,023 citation statements)

References 27 publications

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“…It is known that both single-layer WSe 2 and MoS 2 exhibit direct band gaps, whereas their bulk and homo-bilayer counterparts are indirect (1,27). In agreement with previous work we observe strong excitonic PL peaks at 1.64 eV and 1.87 eV for single-layer WSe 2 and MoS 2 , respectively (Fig.…”

supporting

confidence: 92%

Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides

Fang

Battaglia

Carraro

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

1,034

954

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Significance A new class of heterostructures consisting of layered transition metal dichalcogenide components can be designed and built by van der Waals (vdW) stacking of individual monolayers into functional multilayer structures. Nonetheless, the optoelectronic properties of this new type of vdW heterostructure are unknown. Here, we investigate artificial semiconductor heterostructures built from single-layer WSe 2 and MoS 2 . We observe spatially direct absorption but spatially indirect emission in this heterostructure, with strong interlayer coupling of charge carriers. The coupling at the hetero-interface can be readily tuned by inserting hexagonal BN dielectric layers into the vdW gap. The generic nature of this interlayer coupling is expected to yield a new family of semiconductor heterostructures having tunable optoelectronic properties through customized composite layers.

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supporting

confidence: 92%

Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides

Fang

Battaglia

Carraro

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

1,034

954

View full text Add to dashboard Cite

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“…This coupling is much stronger than (comparable to) the interlayer hopping in WX 2 (MoX 2 ) as listed in Table 1, and it originates from the strong spin-orbit interaction in the d orbitals of the metal atoms. A direct consequence is that the interlayer hopping is virtually suppressed as observed in WX 2 multilayers 25 . At each wavevector q, the eigenstates of equation 2 are two spin doublets separated by a large energy 2 ffiffiffiffiffiffiffiffiffiffiffiffiffiffi…”

Section: Resultsmentioning

confidence: 92%

“…The strong PL peak associated with this transition suggests high efficiency of the injection 21,22,24,25 and remain open questions. Notably, for holes near K points, spin flip…”

Section: Discussionmentioning

confidence: 99%

Magnetoelectric effects and valley-controlled spin quantum gates in transition metal dichalcogenide bilayers

et al. 2013

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In monolayer group-VI transition metal dichalcogenides, charge carriers have spin and valley degrees of freedom, both associated with magnetic moments. On the other hand, the layer degree of freedom in multilayers is associated with electrical polarization. Here we show that transition metal dichalcogenide bilayers offer an unprecedented platform to realize a strong coupling between the spin, valley and layer pseudospin of holes. Such coupling gives rise to the spin Hall effect and spin-dependent selection rule for optical transitions in inversion symmetric bilayer and leads to a variety of magnetoelectric effects permitting quantum manipulation of these electronic degrees of freedom. Oscillating electric and magnetic fields can both drive the hole spin resonance where the two fields have valley-dependent interference, making an interplay between the spin and valley as information carriers possible for potential valley-spintronic applications. We show how to realize quantum gates on the spin qubit controlled by the valley bit.

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“…On the other side, the band edge at K(K′) valleys mainly constructed from d orbits of the heavy metal atoms inherits the strong spin-orbit coupling (SOC) of atomic orbits. And, the Zeeman-like SOC originating from D 1 3h symmetry of monolayer TMDs lifts the out-of-plane spin degeneracy of the band edges at K and K′ valleys by a significant amount, around 0.16 and 0.45 eV in the valence bands of molybdenum dichalcogenides and tungsten dichalcogenides, respectively, and about 1 order of magnitude smaller in conduction bands (10,(21)(22)(23)(24)(25)(26)(27). Owing to the presence of timereversal symmetry ðK ↔ − KÞ, the spin splitting has opposite sign between K and K′ valleys at monolayer TMDs as illustrated in Fig.…”

mentioning

confidence: 99%

Manipulating spin-polarized photocurrents in 2D transition metal dichalcogenides

Xie

Cui

2016

Proc. Natl. Acad. Sci. U.S.A.

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Manipulating spin polarization of electrons in nonmagnetic semiconductors by means of electric fields or optical fields is an essential theme of the conceptual nonmagnetic semiconductor-based spintronics. Here we experimentally demonstrate an electric method of detecting spin polarization in monolayer transition metal dichalcogenides (TMDs) generated by circularly polarized optical pumping. The spin-polarized photocurrent is achieved through the valleydependent optical selection rules and the spin-valley locking in monolayer WS 2 , and electrically detected by a lateral spin-valve structure with ferromagnetic contacts. The demonstrated long spinvalley lifetime, the unique valley-contrasted physics, and the spinvalley locking make monolayer WS 2 an unprecedented candidate for semiconductor-based spintronics.monolayer transition metal dichalcogenides | spin-valley coupling | spintronics | spin lifetime | valley lifetime A longtime focus in nonmagnetic semiconductor spintronics research is to explore methods to generate and manipulate spin of electrons by means of electric fields or optical fields instead of magnetic fields, enabling scalable and integrated devices (1). The present efforts follow two distinct paths. One uses spin Hall effect or optical pumping in III-V semiconductors which feature a significant spin-orbit coupling in a form of Dresselhaus and/or Rashba terms (2-4); the other focuses on spin transport [usually generated by spin injection from ferromagnetic (FM) electrodes] in semiconductor structures made of silicon (5), carbon nanotube (6), graphene (7), etc. which have long spin-coherence length due to weak spin-orbit coupling. The emergence of atomic two-dimensional group VI transition metal dichalcogenides (TMDs) MX 2 (M = Mo, W; X = S, Se), featuring nonzero but contrasting Berry curvatures at inequivalent K and K′ (equivalent to −K) valleys and unique spin-valley locking, provides an alternative pathway toward spintronics (8).Valleys refer to the energy extremes around the high symmetry points of the Brillouin zone, either a "valley" in the conduction band or a "hill" in the valence band. Owing to their hexagonal lattices, the family of TMDs has degenerate but inequivalent K(K′) valleys well separated in the first Brillouin zone. This gives electrons an extra valley degree of freedom, in addition to charge and spin. In monolayer TMDs the inversion symmetry breaking of crystal structures gives rise to nonzero but contrasting Berry curvatures at K and K′ valley which are a characteristic of the Bloch bands and could be recognized as a form of orbital magnetic moment of Bloch electrons (9-11). These contrasting Berry curvatures of electrons (holes) at K(K′) valleys lead to contrasting response to certain stimulus (9-19). One example is the valley Hall effect: An electric field would drive the electrons at different valleys (K and K′) toward opposite transverse directions, in a similar way as in spin Hall effect (10,20). A more pronounced manifestation is valley-dependent circular optical selectio...

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Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides

Cited by 956 publications

References 27 publications

Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides

Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides

Magnetoelectric effects and valley-controlled spin quantum gates in transition metal dichalcogenide bilayers

Manipulating spin-polarized photocurrents in 2D transition metal dichalcogenides

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