Optical generation of excitonic valley coherence in monolayer WSe2.

By Aaron M. Jones, Hongyi Yu, N. Ghimire, Sanfeng Wu, G. Aivazian, J. Ross, Bo Zhao, Jiaqiang Yan, D. Mandrus, Di Xiao and 2 more. Nature Nanotechnology, 2013

1,322 citations recorded by the source corpus.

As a consequence of degeneracies arising from crystal symmetries, it is possible for electron states at band-edges ('valleys') to have additional spin-like quantum numbers. An important question is whether coherent manipulation can be performed on such valley pseudospins, analogous to that implemented using true spin, in the quest for quantum technologies. Here, we show that valley coherence can be generated and detected. Because excitons in a single valley emit circularly polarized photons, linear polarization can only be generated through recombination of an exciton in a coherent superposition of the two valley states. Using monolayer semiconductor WSe2 devices, we first establish the circularly polarized optical selection rules for addressing individual valley excitons and trions. We then demonstrate coherence between valley excitons through the observation of linearly polarized luminescence, whose orientation coincides with that of the linearly polarized excitation, for any given polarization angle. In contrast, the corresponding photoluminescence from trions is not observed to be linearly polarized, consistent with the expectation that the emitted photon polarization is entangled with valley pseudospin. The ability to address coherence, in addition to valley polarization, is a step forward towards achieving quantum manipulation of the valley index necessary for coherent valleytronics.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/bf0d3e6f77667dd992aa50dab36f8978fb2a93f0

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Citations in the corpus

Excitonic linewidth approaching the homogeneous limit in MoS2-based van der Waals heterostructures (2017, methodology): “Detailed studies of valley polarization and coherence have so far mainly focused on ML WSe2, due to the comparatively narrow linewidth and high polarization degree of the emission [26,79].”
Direct observation of spin-polarized bulk bands in an inversion-symmetric semiconductor (2014, background): “spin canting away from the band extrema, which may explain the loss in the degree of valley polarisation that can be induced with increasing energy of photoexcitation.(7,25) More generally, our experimental realisation of a system where bulk inversion symmetry breaking is not a necessary condition t”
Spin-orbit coupling, quantum dots, and qubits in monolayer transition metal dichalcogenides (2013, neutral): “3”
The effect of the substrate on the Raman and photoluminescence emission of single-layer MoS2 (2013, positive): “Photoluminescence from monolayers TMDCs has been extensively studied and it proved to be a valuable tool to gain insight in intrinsic material properties [7, 8, 11, 13, 41].”