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Enhanced valley splitting in monolayer WSe2 due to magnetic exchange field

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.

References

  1. Xiao, D., Liu, G.-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).

    Article  Google Scholar 

  2. Zhu, Z., Cheng, Y. & Schwingenschlögl, U. Giant spin-orbit-induced spin splitting in two-dimensional transition-metal dichalcogenide semiconductors. Phys. Rev. B 84, 153402 (2011).

    Article  Google Scholar 

  3. Cao, T. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nat. Commun. 3, 887 (2012).

    Article  Google Scholar 

  4. Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nat. Nanotechnol. 7, 494–498 (2012).

    CAS  Article  Google Scholar 

  5. Zeng, H. L., Dai, J. F., Yao, W., Xiao, D. & Cui, X. D. Valley polarization in MoS2 monolayers by optical pumping. Nat. Nanotechnol. 7, 490–493 (2012).

    CAS  Article  Google Scholar 

  6. Li, Y. et al. Valley splitting and polarization by the Zeeman effect in monolayer MoSe2 . Phys. Rev. Lett. 113, 266804 (2014).

    Article  Google Scholar 

  7. Aivazian, G. et al. Magnetic control of valley pseudospin in monolayer WSe2 . Nat. Phys. 11, 148–152 (2015).

    CAS  Article  Google Scholar 

  8. MacNeill, D. et al. Breaking of valley degeneracy by magnetic field in monolayer MoSe2 . Phys. Rev. Lett. 114, 037401 (2015).

    Article  Google Scholar 

  9. Srivastava, A. et al. Valley Zeeman effect in elementary optical excitations of monolayer WSe2 . Nat. Phys. 11, 141–147 (2015).

    CAS  Article  Google Scholar 

  10. Zhang, Q. Y., Yang, S. Y. A., Mi, W. B., Cheng, Y. C. & Schwingenschlögl, U. Large spin-valley polarization in monolayer MoTe2 on top of EuO(111). Adv. Mater. 28, 959–966 (2016).

    CAS  Article  Google Scholar 

  11. Qi, J. S., Li, X., Niu, Q. & Feng, J. Giant and tunable valley degeneracy splitting in MoTe2 . Phys. Rev. B 92, 121403 (2015).

    Article  Google Scholar 

  12. Rohling, N., Russ, M. & Burkard, G. Hybrid spin and valley quantum computing with singlet-triplet qubits. Phys. Rev. Lett. 113, 176801 (2014).

    Article  Google Scholar 

  13. Matte, H. S. et al. MoS2 and WS2 analogues of graphene. Angew. Chem. Int. Ed. 49, 4059–4062 (2010).

    CAS  Article  Google Scholar 

  14. Zhao, W. et al. Evolution of electronic structure in atomically thin sheets of WS2 and WSe2 . ACS Nano 7, 791–797 (2013).

    CAS  Article  Google Scholar 

  15. Yuan, H. T. et al. Generation and electric control of spin-valley-coupled circular photogalvanic current in WSe2 . Nat. Nanotechnol. 9, 851–857 (2014).

    CAS  Article  Google Scholar 

  16. Eginligil, M. et al. Dichroic spin-valley photocurrent in monolayer molybdenum disulphide. Nat. Commun. 6, 7636 (2015).

    Article  Google Scholar 

  17. Lee, J., Mak, K. F. & Shan, J. Electrical control of the valley Hall effect in bilayer MoS2 transistors. Nat. Nanotechnol. 11, 421–425 (2016).

    CAS  Article  Google Scholar 

  18. Mak, K. F., McGill, K. L., Park, J. & McEuen, P. L. The valley Hall effect in MoS2 transistors. Science 344, 1489–1492 (2014).

    CAS  Article  Google Scholar 

  19. Scrace, T. et al. Magnetoluminescence and valley polarized state of a two-dimensional electron gas in WS2 monolayers. Nat. Nanotechnol. 10, 603–607 (2015).

    CAS  Article  Google Scholar 

  20. Yuan, H. T. et al. Zeeman-type spin splitting controlled by an electric field. Nat. Phys. 9, 563–569 (2013).

    CAS  Article  Google Scholar 

  21. Ye, Y. et al. Electrical generation and control of the valley carriers in a monolayer transition metal dichalcogenide. Nat. Nanotechnol. 11, 598–602 (2016).

    CAS  Article  Google Scholar 

  22. Stier, A. V., McCreary, K. M., Jonker, B. T., Kono, J. & Crooker, S. A. Exciton diamagnetic shifts and valley Zeeman effects in monolayer WS2 and MoS2 to 65 Tesla. Nat. Commun. 7, 10643 (2016).

    CAS  Article  Google Scholar 

  23. Koperski, M. et al. Single photon emitters in exfoliated WSe2 structures. Nat. Nanotechnol. 10, 503–506 (2015).

    CAS  Article  Google Scholar 

  24. Sie, E. J. et al. Valley-selective optical Stark effect in monolayer WS2 . Nat. Mater. 14, 290–294 (2015).

    CAS  Article  Google Scholar 

  25. Kim, J. et al. Ultrafast generation of pseudo-magnetic field for valley excitons in WSe2 monolayers. Science 346, 1205–1208 (2014).

    CAS  Article  Google Scholar 

  26. Moodera, J. S., Santos, T. S. & Nagahama, T. The phenomena of spin-filter tunnelling. J. Phys-Condens. Mat. 19, 165202 (2007).

    Article  Google Scholar 

  27. Korenev, V. Optical orientation in ferromagnet/semiconductor hybrids. Semiconductor Sci. Technol. 23, 114012 (2008).

    Article  Google Scholar 

  28. Wei, P. et al. Strong interfacial exchange field in the graphene/EuS heterostructure. Nat. Mater. 15, 711–716 (2016).

    CAS  Article  Google Scholar 

  29. Wang, Z., Tang, C., Sachs, R., Barlas, Y. & Shi, J. Proximity-induced ferromagnetism in graphene revealed by the anomalous Hall effect. Phys. Rev. Lett. 114, 016603 (2015).

    Article  Google Scholar 

  30. Katmis, F. et al. A high-temperature ferromagnetic topological insulating phase by proximity coupling. Nature 533, 513–516 (2016).

    CAS  Article  Google Scholar 

  31. Lazic, P., Belashchenko, K. D. & Zutic, I. Effective gating and tunable magnetic proximity effects in two-dimensional heterostructure. Phys. Rev. B 93, 241401 (2016).

    Article  Google Scholar 

  32. He, K. L. et al. Tightly bound excitons in monolayer WSe2 . Phys. Rev. Lett. 113, 026803 (2014).

    Article  Google Scholar 

  33. Li, C. H. et al. Spin injection across (110) interfaces: Fe/GaAs(110) spin-light-emitting diodes. Appl. Phys. Lett. 85, 1544–1546 (2004).

    CAS  Article  Google Scholar 

  34. Taheri, P. et al. Growth mechanism of largescale MoS2 monolayer by sulfurization of MoO3 film. Mater. Res. Express 3, 075009 (2016).

    Article  Google Scholar 

  35. Gurarslan, A. et al. Surface-energy-assisted perfect transfer of centimeter-scale monolayer and few-layer MoS2 films onto arbitrary substrates. ACS Nano 8, 11522–11528 (2014).

    CAS  Article  Google Scholar 

Download references

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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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.

Corresponding author

Correspondence to Hao Zeng.

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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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