Electrical generation and control of the valley carriers in a monolayer transition metal dichalcogenide


Electrically controlling the flow of charge carriers is the foundation of modern electronics. By accessing the extra spin degree of freedom (DOF) in electronics, spintronics allows for information processes such as magnetoresistive random-access memory1. Recently, atomic membranes of transition metal dichalcogenides (TMDCs) were found to support unequal and distinguishable carrier distribution in different crystal momentum valleys. This valley polarization of carriers enables a new DOF for information processing2,3,4. A variety of valleytronic devices such as valley filters and valves have been proposed5, and optical valley excitation has been observed2,3,4. However, to realize its potential in electronics it is necessary to electrically control the valley DOF, which has so far remained a significant challenge. Here, we experimentally demonstrate the electrical generation and control of valley polarization. This is achieved through spin injection via a diluted ferromagnetic semiconductor and measured through the helicity of the electroluminescence due to the spin–valley locking in TMDC monolayers6. We also report a new scheme of electronic devices that combine both the spin and valley DOFs. Such direct electrical generation and control of valley carriers opens up new dimensions in utilizing both the spin and valley DOFs for next-generation electronics and computing.

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Figure 1: Electrically driven valley polarization via spin injection and the principle of operation.
Figure 2: Electroluminescence of the monolayer WS2/(Ga,Mn)As heterojunctions.
Figure 3: Electrical control of valley polarization in monolayer WS2.
Figure 4: Valley dynamics measurement in monolayer WS2 on (Ga,Mn)As.


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The authors acknowledge financial support from Office of Naval Research Multidisciplinary University Research Initiative program under grant no. N00014-13-1-0649, and National Science Foundation (EFMA-1542741). J.Z. and H.W. acknowledge support from MOST of China (grant no. 2015CB921503) and NSFC (grant no. 61334006). Y.Y. thanks T. Cao of the University of California, Berkeley for helpful discussions.

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Y.Y., X.Y., Z.Y. and X.Z. conceived the project. H.W. and J.Z. grew and characterized (Ga,Mn)As films. Y.Y., H.Z. and M.Z. developed the sample design and fabricated the samples. Y.Y., J.X. and Z.Y. performed the measurements. Y.Y. and J.X. carried out the data analysis. Y.Y., X.Y. and J.X. wrote the manuscript. X.Z., X.Y. and Y.W. guided the research. All authors discussed the results and commented on the manuscript.

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Correspondence to Xiang Zhang.

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Ye, Y., Xiao, J., Wang, H. et al. Electrical generation and control of the valley carriers in a monolayer transition metal dichalcogenide. Nature Nanotech 11, 598–602 (2016). https://doi.org/10.1038/nnano.2016.49

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