Letter | Published:

Enhanced valley splitting in monolayer WSe2 due to magnetic exchange field

Nature Nanotechnology volume 12, pages 757762 (2017) | Download Citation

Abstract

Exploiting the valley degree of freedom to store and manipulate information provides a novel paradigm for future electronics. A monolayer transition-metal dichalcogenide (TMDC) with a broken inversion symmetry possesses two degenerate yet inequivalent valleys1,2, which offers unique opportunities for valley control through the helicity of light3,4,5. Lifting the valley degeneracy by Zeeman splitting has been demonstrated recently, which may enable valley control by a magnetic field6,7,8,9. However, the realized valley splitting is modest (0.2 meV T–1). Here we show greatly enhanced valley spitting in monolayer WSe2, utilizing the interfacial magnetic exchange field (MEF) from a ferromagnetic EuS substrate. A valley splitting of 2.5 meV is demonstrated at 1 T by magnetoreflectance measurements and corresponds to an effective exchange field of 12 T. Moreover, the splitting follows the magnetization of EuS, a hallmark of the MEF. Utilizing the MEF of a magnetic insulator can induce magnetic order and valley and spin polarization in TMDCs, which may enable valleytronic and quantum-computing applications10,11,12.

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Acknowledgements

This work was supported by US National Science Foundation (MRI-1229208, DMR-1104994 and CBET-1510121), the Natural Sciences and Engineering Research Council of Canada Discovery grant RGPIN 418415-2012, the National Natural Science Foundation of China (nos 11504169, and 61575094) and the Unity Through Knowledge Fund, Contract No. 22/15. We thank Q. Niu, X. Li (University of Texas at Austin) and I. Zutic (University of Buffalo) for the insightful discussions.

Author information

Affiliations

  1. Department of Physics, University at Buffalo, State University of New York, Buffalo, New York 14260, USA

    • Chuan Zhao
    • , Tenzin Norden
    • , Peiyao Zhang
    • , Puqin Zhao
    • , Fan Sun
    • , James P. Parry
    • , Payam Taheri
    • , Thomas Scrace
    • , Kaifei Kang
    • , Athos Petrou
    •  & Hao Zeng
  2. Key Laboratory of Flexible Electronics and Institute of Advanced Materials, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Technical University, Nanjing 211816, China

    • Puqin Zhao
    • , Yingchun Cheng
    •  & Wei Huang
  3. School of Science, MOE Key Laboratory of Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an Jiaotong University, Xi'an 710049, China

    • Jieqiong Wang
    • , Kaifei Kang
    • , Sen Yang
    •  & Hao Zeng
  4. Institute of Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada

    • Yihang Yang
    •  & Guo-xing Miao
  5. Department of Physics, University of Nebraska-Omaha, Omaha, Nebraska 68182, USA

    • Renat Sabirianov
  6. Department of Material Science and Technology, University of Crete, Heraklion, GR 71003, Greece

    • George Kioseoglou

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Contributions

H.Z. and A.P. conceived and designed experiments. C.Z., P.-Q.Z., P.T., K.K. and J.W. prepared and characterized the monolayer TMDCs, including WSe2, and transferred them onto EuS substrates. P.Z., T.N., C.Z., T.S. and A.P. performed magneto-optical measurements and data analysis. Y.Y. and G.M. provided the EuS thin films. F.S. performed magnetic measurements of EuS. R.S. and Y.C. performed the first-principle calculations. H.Z., C.Z., Y.C., R.S. G.K. and A.P. wrote the manuscript. All the authors commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Hao Zeng.

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DOI

https://doi.org/10.1038/nnano.2017.68

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