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Valley- and spin-polarized Landau levels in monolayer WSe2

Nature Nanotechnology volume 12, pages 144–149 (2017)Cite this article

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Abstract

Electrons in monolayer transition metal dichalcogenides are characterized by valley and spin quantum degrees of freedom, making it possible to explore new physical phenomena and to foresee novel applications in the fields of electronics and optoelectronics. Theoretical proposals further suggest that Berry curvature effects, together with strong spin–orbit interactions, can generate unconventional Landau levels (LLs) under a perpendicular magnetic field. In particular, these would support valley- and spin-polarized chiral edge states in the quantum Hall regime. However, this unique LL structure has not been observed experimentally in transition metal dichalcogenides. Here we report the observation of fully valley- and spin-polarized LLs in high-quality WSe2 monolayers achieved by exploiting a van der Waals heterostructure device platform. We applied handedness-resolved optical reflection spectroscopy to probe the inter-LL transitions at individual valleys and derived the LL structure in turn. We also measured a sizeable doping-induced mass renormalization driven by the strong Coulomb interactions.

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Figure 1: Optical transitions in dual-gated monolayer WSe2.
Figure 2: Valley-contrasting inter-LL transitions.
Figure 3: Magnetic-field dispersion of valley- and spin-polarized LLs.
Figure 4: LL structure of monolayer WSe2.

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Acknowledgements

The experimental research was supported by the National Science Foundation through grant numbers DMR-1410407 and 1420451 (for sample and device fabrication) and the Air Force Office of Scientific Research under grant no. FA9550-14-1-0268 (spectroscopy in high fields). Support for data analysis was provided by the US Department of Energy, Office of Basic Energy Sciences under award no. DESC0012635 (J.S.) and the Air Force Office of Scientific Research under grant FA9550-16-1-0249 (K.F.M.).

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Authors and Affiliations

  1. Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, 16802-6300, Pennsylvania, USA

    Zefang Wang, Jie Shan & Kin Fai Mak

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  1. Zefang Wang
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  2. Jie Shan
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Contributions

J.S. and K.F.M. conceived and designed the experiments. Z.W. performed the experiments. All authors contributed to the analysis and interpretation of results and preparation of the manuscript.

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Correspondence to Jie Shan or Kin Fai Mak.

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The authors declare no competing financial interests.

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Wang, Z., Shan, J. & Mak, K. Valley- and spin-polarized Landau levels in monolayer WSe2. Nature Nanotech 12, 144–149 (2017). https://doi.org/10.1038/nnano.2016.213

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