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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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.
The authors declare no competing financial interests.
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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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