Abstract
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 numbers1,2,3,4,5,6. 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 technologies7,8. 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 coherence9,10, in addition to valley polarization11,12,13,14,15, is a step forward towards achieving quantum manipulation of the valley index necessary for coherent valleytronics.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Xiao, D., Liu, G-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).
Zhu, Z., Collaudin, A., Fauque, B., Kang, W. & Behnia, K. Field-induced polarization of Dirac valleys in bismuth. Nature Phys. 8, 89–94 (2012).
Rycerz, A., Tworzydlo, J. & Beenakker, C. W. J. Valley filter and valley valve in graphene. Nature Phys. 3, 172–175 (2007).
Bishop, N. C. et al. Valley polarization and susceptibility of composite fermions around a filling factor ν = 3/2. Phys. Rev. Lett. 98, 266404 (2007).
Gunawan, O. et al. Valley susceptibility of an interacting two-dimensional electron system. Phys. Rev. Lett. 97, 186404 (2006).
Gunawan, O., Habib, B., De Poortere, E. P. & Shayegan, M. Quantized conductance in an AlAs two-dimensional electron system quantum point contact. Phys. Rev. B 74, 155436 (2006).
Gupta, J. A., Knobel, R., Samarth, N. & Awschalom, D. D. Ultrafast manipulation of electron spin coherence. Science 292, 2458–2461 (2001).
Press, D., Ladd, T. D., Zhang, B. & Yamamoto, Y. Complete quantum control of a single quantum dot spin using ultrafast optical pulses. Nature 456, 218–221 (2008).
Laird, E. A., Pei, F. & Kouwenhoven, L. P. A valley–spin qubit in a carbon nanotube. Preprint at http://lanl.arXiv.org/1210.3085 (2012).
Pályi, A. & Burkard, G. Disorder-mediated electron valley resonance in carbon nanotube quantum dots. Phys. Rev. Lett. 106, 086801 (2011).
Cao, T. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nature Commun. 3, 887 (2012).
Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nature Nanotech. 7, 494–498 (2012).
Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nature Nanotech. 7, 490–493 (2012).
Sallen, G. et al. Robust optical emission polarization in MoS2 monolayers through selective valley excitation. Phys. Rev. B 86, 081301 (2012).
Wu, S. et al. Electrical tuning of valley magnetic moment through symmetry control in bilayer MoS2 . Nature Phys. 9, 149–153 (2013).
Novoselov, K. S. et al. Two-dimensional atomic crystals. Proc. Natl Acad. Sci. USA 102, 10451–10453 (2005).
Mak, K. F., Lee, C., Hone, J., Shan, J. & Heinz, T. F. Atomically thin MoS2: a new direct-gap semiconductor. Phys. Rev. Lett. 105, 136805 (2010).
Splendiani, A. et al. Emerging photoluminescence in monolayer MoS2 . Nano Lett. 10, 1271–1275 (2010).
Ross, J. S. et al. Electrical control of neutral and charged excitons in a monolayer semiconductor. Nature Commun. 4, 1474 (2013).
Mak, K. F. et al. Tightly bound trions in monolayer MoS2 . Nature Mater. 12, 207–211 (2013).
Coehoorn, R., Haas, C. & de Groot, R. A. Electronic structure of MoSe2, MoS2, and WSe2. II. The nature of the optical band gaps. Phys. Rev. B 35, 6203–6206 (1987).
Zhao, W. et al. Evolution of electronic structure in atomically thin sheets of WS2 and WSe2 . ACS Nano 7, 791–797 (2013).
Kheng, K. et al. Observation of negatively charged excitons X− in semiconductor quantum wells. Phys. Rev. Lett. 71, 1752–1755 (1993).
Miller, D. A. B. et al. Band-edge electroabsorption in quantum well structures: the quantum-confined Stark effect. Phys. Rev. Lett. 53, 2173–2176 (1984).
Misewich, J. A. et al. Electrically induced optical emission from a carbon nanotube FET. Science 300, 783–786 (2003).
Lefebvre, J., Fraser, J. M., Finnie, P. & Homma, Y. Photoluminescence from an individual single-walled carbon nanotube. Phys. Rev. B 69, 075403 (2004).
Bayer, M. et al. Electron and hole g factors and exchange interaction from studies of the exciton fine structure in In0.6Ga0.4As quantum dots. Phys. Rev. Lett. 82, 1748–1751 (1999).
Bonnot, A., Planel, R. & à la Guillaume, C. B. Optical orientation of excitons in CdS. Phys. Rev. B 9, 690–702 (1974).
Amand, T. et al. Spin quantum beats of 2D excitons. Phys. Rev. Lett. 78, 1355–1358 (1997).
Mohan, A. et al. Polarization-entangled photons produced with high-symmetry site-controlled quantum dots. Nature Photon. 4, 302–306 (2010).
Dousse, A. et al. Ultrabright source of entangled photon pairs. Nature 466, 217–220 (2010).
Gibbs, H. M., Khitrova, G. & Koch, S. W. Exciton–polariton light–semiconductor coupling effects. Nature Photon. 5, 273–273 (2011).
Maialle, M. Z., de Andrada e Silva, E. A. & Sham, L. J. Exciton spin dynamics in quantum wells. Phys. Rev. B 47, 15776–15788 (1993).
Acknowledgements
The authors thank B. Spivak, D. Cobden, A. Andreev and K-M. Fu for helpful discussions. This work was mainly supported by the National Science Foundation (NSF, DMR-1150719). The experimental set-up and device fabrication was partially supported by a Defense Advanced Research Projects Agency (DARPA) Young Faculty Award (YFA) (N66001-11-1-4124). H.Y. and W.Y. were supported by the Research Grant Council (HKU705513P) and the University Grant Council (AoE/P-04/08) of the government of Hong Kong, and the Croucher Foundation under the Croucher Innovation Award. N.G., J.Y., D.M. and D.X. were supported by the US Department of Energy (DoE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division. Device fabrication was performed at the University of Washington Microfabrication Facility and the NSF-funded Nanotech User Facility.
Author information
Authors and Affiliations
Contributions
X.X. conceived the experiments. A.M.J. performed the experiments, assisted by S.W., G.A. and B.Z. The devices were fabricated by J.S.R., assisted by A.M.J. The theoretical explanation was provided by H.Y. and W.Y., with input from D.X. The WSe2 crystals were synthesized by N.J.G., J.Y. and D.G.M., who also performed bulk characterization measurements. A.M.J., X.X., H.Y. and W.Y. co-wrote the paper. All authors discussed the results and commented on the manuscript.
Corresponding authors
Ethics declarations
Competing interests
The authors declare no competing financial interests.
Supplementary information
Supplementary information
Supplementary information (PDF 1855 kb)
Rights and permissions
About this article
Cite this article
Jones, A., Yu, H., Ghimire, N. et al. Optical generation of excitonic valley coherence in monolayer WSe2. Nature Nanotech 8, 634–638 (2013). https://doi.org/10.1038/nnano.2013.151
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/nnano.2013.151
This article is cited by
-
Dynamically tunable moiré exciton Rydberg states in a monolayer semiconductor on twisted bilayer graphene
Nature Materials (2024)
-
Inheritance of the exciton geometric structure from Bloch electrons in two-dimensional layered semiconductors
Frontiers of Physics (2024)
-
Excitonic devices based on two-dimensional transition metal dichalcogenides van der Waals heterostructures
Frontiers of Chemical Science and Engineering (2024)
-
Chemomechanical modification of quantum emission in monolayer WSe2
Nature Communications (2023)
-
Room temperature valley polarization via spin selective charge transfer
Nature Communications (2023)