Intervalley Scattering and Localization Behaviors of Spin-Valley Coupled Dirac Fermions

Lu, Hai-Zhou; Yao, Wang; Xiao, Di; Shen, Shun-Qing

doi:10.1103/physrevlett.110.016806

Cited by 169 publications

(126 citation statements)

References 41 publications

(68 reference statements)

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“…Reference [39] shows that this mechanism requires a ∼ k 4 dependence on hole momentum, which leads to a stronger temperature dependence (T 2 ) than our observation. Relaxation through flexural phonon modes was also considered as a potential mechanism [44].…”

Section: Introductioncontrasting

confidence: 49%

Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy

et al. 2014

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We measured the lifetime of optically created valley polarization in single layer WS 2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). However the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single layer WS 2 . One process involves direct scattering of excitons from K to K valleys with a spin flip-flop interaction. The other mechanism involves scattering through spin degenerate Γ valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Γ and K valleys.

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Section: Introductioncontrasting

confidence: 49%

Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy

et al. 2014

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“…Our results also differ from earlier reports on bulk MoS 2 where no crossover was observed with temperature [21][22][23] . This observation of WAL at fields of B ∼ 3 T and above is somewhat surprising in light of recent theoretical papers 10,20 which predict the exact opposite, i.e. WAL at low fields and WL at larger fields.…”

mentioning

confidence: 65%

Quantum Transport and Observation of Dyakonov-Perel Spin-Orbit Scattering in MonolayerMoS2

et al. 2016

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Monolayers of group 6 transition metal dichalcogenides are promising candidates for future spin-, valley-, and charge-based applications. Quantum transport in these materials reflects a complex interplay between real spin and pseudo-spin (valley) relaxation processes, which leads to either positive or negative quantum correction to the classical conductivity. Here we report experimental observation of a crossover from weak localization to weak anti-localization in highly n-doped monolayer MoS2. We show that the crossover can be explained by a single parameter associated with electron spin lifetime of the system. We find that the spin lifetime is inversely proportional to momentum relaxation time, indicating that spin relaxation occurs via Dyakonov-Perel mechanism.PACS numbers: 73.20.Fz, Quasi-two-dimensional (2D) crystals of group 6 transition metal dichalcogenides (TMDs)1-3 such as MoS 2 and WSe 2 have been recognized as a new class of semiconductors for spintronics and valleytronics 4,5 . Due to distinct crystal symmetry and strong spin-orbit coupling, monolayer MoS 2 and other group 6 TMDs exhibit spin-split degenerate valleys at the corners (K and K' points) of the Brillouin zone. Since the spin and the valley degrees of freedom are coupled via time reversal symmetry, the valley degree of freedom can be accessed optically by circularly polarized light 6,7 . A recent study has also shown that valley polarization can be electrically detected as anomalous Hall voltage arising from valley Hall effect 8 . The exploitation of coupled spin and valley degrees of freedom is an intriguing approach to enabling novel spintronic and valleytronic device concepts 4 .The use of spin-and valley-polarized charges as information carriers requires that the polarization state be preserved over a sufficiently long period. While recent experimental studies found the valley lifetime of optically generated excitons to be on the order of nanoseconds 7 , little is known about the relaxtion lifetime in unipolar charge transport. In this regard, quantum transport 9,10 has been suggested as an effective probe to study the dynamics of scattering processes that lead to loss of spin and valley polarization.Unlike the Drude-Boltzmann semi-classical transport, the quantum corrections to the conductivity are interference effects, and are therefore universal in the sense that they should not depend on the details of the microscopic mechanisms at play. However, as discussed in literature 11 , there is a long tradition of extracting information about the underlying microscopic mechanisms from the quantum transport. For example, in GaAs heterostructures the quantum interference correction to the classical conductivity is determined by the breaking of spin-rotational symmetry by spin-orbit coupling 12 . But since the spin-relaxation rate changes with carrier density, Miller et al.13 observed a crossover from pure weak localization (WL) at low carrier density to pure weak anti-localization (WAL) at high carrier density. A similar phenomenon has been...

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“…18 where the valley-spin coupled physics is first predicted in monolayer MX 2 , an effective two-band k·p model is given based on symmetry considerations, which suggests that the band edge electrons and holes can be described as massive Dirac fermions. This k · p model has also been applied to study the transport, optical, and magnetic properties of MX 2 monolayers [25][26][27] and bilayers. 22,28 However, the k · p model is only valid close to the band edge.…”

Section: Introductionmentioning

confidence: 99%

Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides

et al. 2013

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We present a three-band tight-binding (TB) model for describing the low-energy physics in monolayers of group-VIB transition metal dichalcogenides MX2 (M =Mo, W; X=S, Se, Te). As the conduction and valence band edges are predominantly contributed by the d z 2 , dxy, and d x 2 −y 2 orbitals of M atoms, the TB model is constructed using these three orbitals based on the symmetries of the monolayers. Parameters of the TB model are fitted from the first-principles energy bands for all MX2 monolayers. The TB model involving only the nearest-neighbor M -M hoppings is sufficient to capture the band-edge properties in the ±K valleys, including the energy dispersions as well as the Berry curvatures. The TB model involving up to the third-nearest-neighbor M -M hoppings can well reproduce the energy bands in the entire Brillouin zone. Spin-orbit coupling in valence bands is well accounted for by including the on-site spin-orbit interactions of M atoms. The conduction band also exhibits a small valley-dependent spin splitting which has an overall sign difference between MoX2 and WX2. We discuss the origins of these corrections to the three-band model. The three-band TB model developed here is efficient to account for low-energy physics in MX2 monolayers, and its simplicity can be particularly useful in the study of many-body physics and physics of edge states.

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Intervalley Scattering and Localization Behaviors of Spin-Valley Coupled Dirac Fermions

Cited by 169 publications

References 41 publications

Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy

Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy

Quantum Transport and Observation of Dyakonov-Perel Spin-Orbit Scattering in MonolayerMoS2

Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides

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