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Enhanced valley splitting in monolayer WSe2 due to magnetic exchange field

Nature Nanotechnology volume 12, pages 757–762 (2017)Cite this article

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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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Figure 1: Schematic diagrams of the WSe2 monolayer on the substrates.
Figure 2: Measured valley splitting ΔE as a function of magnetic field.
Figure 3: Comparing the magnetic-field-dependent valley-exchange splitting of WSe2/EuS and the field-dependent magnetization of EuS measured at different temperatures.
Figure 4: Calculated band structure and valley-exchange splitting of WSe2/EuS.

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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.

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Authors and Affiliations

  1. Department of Physics, University at Buffalo, State University of New York, Buffalo, 14260, New York, 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, 68182, Nebraska, USA

    Renat Sabirianov

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

    George Kioseoglou

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  1. Chuan Zhao
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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.

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Correspondence to Hao Zeng.

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Zhao, C., Norden, T., Zhang, P. et al. Enhanced valley splitting in monolayer WSe2 due to magnetic exchange field. Nature Nanotech 12, 757–762 (2017). https://doi.org/10.1038/nnano.2017.68

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