Most electronic devices exploit the electric charge of electrons, but it is also possible to build devices that rely on other properties of electrons. Spintronic devices, for example, make use of the spin of electrons1,2. Valleytronics is a more recent development that relies on the fact that the conduction bands of some materials have two or more minima at equal energies but at different positions in momentum space3,4,5. To make a valleytronic device it is necessary to control the number of electrons in these valleys, thereby producing a valley polarization6,7,8,9,10,11. Single-layer MoS2 is a promising material for valleytronics because both the conduction and valence band edges have two energy-degenerate valleys at the corners of the first Brillouin zone12. Here, we demonstrate that optical pumping with circularly polarized light can achieve a valley polarization of 30% in pristine monolayer MoS2. Our results, and similar results by Mak et al.13, demonstrate the viability of optical valley control and valley-based electronic and optoelectronic applications in MoS2 monolayers.
Subscribe to Journal
Get full journal access for 1 year
only $4.92 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Wolf, S. A. et al. Spintronics: a spin-based electronics vision for the future. Science 294, 1488–1495 (2001).
Zutic, I., Fabian, J. & Das Sarma, S. Spintronics: fundamentals and applications. Rev. Mod. Phys. 76, 323–410 (2004).
Rycerz, A., Tworzydlo, J. & Beenakker, C. W. J. Valley filter and valley valve in graphene. Nature Phys. 3, 172–175 (2007).
Shkolnikov, Y. P., De Poortere, E. P., Tutuc, E. & Shayegan, M. Valley splitting of AlAs two-dimensional electrons in a perpendicular magnetic field. Phys. Rev. Lett. 89, 226805 (2002).
Xiao, D., Yao, W. & Niu, Q. Valley-contrasting physics in graphene: magnetic moment and topological transport. Phys. Rev. Lett. 99, 236809 (2007).
Zhu, Z., Collaudin, A., Fauque, B., Kang, W. & Behnia, K. Field-induced polarization of Dirac valleys in bismuth. Nature Phys. 8, 89–94 (2012).
Gunawan, O. et al. Valley susceptibility of an interacting two-dimensional electron system. Phys. Rev. Lett. 97, 186404 (2006).
Tombros, N. et al. Quantized conductance of a suspended graphene nanoconstriction. Nature Phys. 7, 697–700 (2011).
Low, T. & Guinea, F. Strain-induced pseudomagnetic field for novel graphene electronics. Nano Lett. 10, 3551–3554 (2010).
Gunlycke, D. & White, C. T. Graphene valley filter using a line defect. Phys. Rev. Lett. 106, 136806 (2011).
Yao, W., Xiao, D. & Niu, Q. Valley-dependent optoelectronics from inversion symmetry breaking. Phys. Rev. B 77, 235406 (2008).
Xiao, D., Liu, G. B., Feng, W., Xu, X. D. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).
Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nature Nanotech. http://dx.doi.org/10.1038/nnano.2012.96 (2012).
Lee, C. et al. Anomalous lattice vibrations of single- and few-layer MoS2 . ACS Nano 4, 2695–2700 (2010).
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).
Cao, T., Feng, J., Shi, J., Niu, Q. & Wang, E. MoS2 as an ideal material for valleytronics: valley-selective circular dichroism and valley Hall effect. Preprint at http://arxiv.org/abs/1112.4013 (2011).
Frindt, R. F. & Yoffe, A. D. Physical properties of layer structures: optical properties and photoconductivity of thin crystals of molybdenum disulphide. Proc. R. Soc. Lond. A 273, 69–83 (1963).
Parsons, R. R. Band-to-band optical pumping in solids and polarized photoluminescence. Phys. Rev. Lett. 23, 1152–1154 (1969).
Dyakonov, M. I. Introduction to spin physics in semiconductors. Physica E 35, 246–250 (2006).
Korn, T., Heydrich, S., Hirmer, M., Schmutzler, J. & Schuller, C. Low-temperature photocarrier dynamics in monolayer MoS2 . Appl. Phys. Lett. 99, 102109 (2011).
Wakabayashi, N., Smith, H. G. & Nicklow, R. M. Lattice dynamics of hexagonal MoS2 studied by neutron scattering. Phys. Rev. B 12, 659–663 (1975).
Jiménez Sandoval, S., Yang, D., Frindt, R. F. & Irwin, J. C. Raman study and lattice dynamics of single molecular layers of MoS2 . Phys. Rev. B 44, 3955–3962 (1991).
The authors thank Bairen Zhu, Lu Xie, Dongmei Deng, J.Q. Ning, C.C. Zheng and S.J. Xu for technical assistance. H.Z., J.D., X.C. and W.Y. were supported by the Research Grant Council (HKU10/CRF/08, HKU701810P, HKU706412P) and the University Grant Council (AoE/P-04/08 and SEG_CUHK06) of the government of HKSAR. D.X. was supported by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
The authors declare no competing financial interests.
About this article
Cite this article
Zeng, H., Dai, J., Yao, W. et al. Valley polarization in MoS2 monolayers by optical pumping. Nature Nanotech 7, 490–493 (2012). https://doi.org/10.1038/nnano.2012.95
Nature Reviews Physics (2021)
Communications Materials (2021)
Room-temperature electron spin polarization exceeding 90% in an opto-spintronic semiconductor nanostructure via remote spin filtering
Nature Photonics (2021)
Deep subwavelength control of valley polarized cathodoluminescence in h-BN/WSe2/h-BN heterostructure
Nature Communications (2021)
Silica optical fiber integrated with two-dimensional materials: towards opto-electro-mechanical technology
Light: Science & Applications (2021)