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Generation and electric control of spin–valley-coupled circular photogalvanic current in WSe2

Abstract

The valley degree of freedom in layered transition-metal dichalcogenides provides an opportunity to extend the functionalities of spintronics and valleytronics devices. The achievement of spin-coupled valley polarization induced by the non-equilibrium charge-carrier imbalance between two degenerate and inequivalent valleys has been demonstrated theoretically and by optical experiments. However, the generation of a valley and spin current with the valley polarization in transition-metal dichalcogenides remains elusive. Here we demonstrate a spin-coupled valley photocurrent, within an electric-double-layer transistor based on WSe2, whose direction and magnitude depend on the degree of circular polarization of the incident radiation and can be further modulated with an external electric field. This room-temperature generation and electric control of a valley and spin photocurrent provides a new property of electrons in transition-metal dichalcogenide systems, and thereby enables additional degrees of control for quantum-confined spintronic devices.

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Figure 1: Schematic diagrams of the CPGE based on Rashba spin splitting, and the crystal/electronic structure of layered 2H-WSe2.
Figure 2: Schematic diagram and incident angle-dependent CPGE measurement of ambipolar WSe2 EDLTs.
Figure 3: Electric field modulation of the spin photocurrent in WSe2 EDLTs.
Figure 4: Light-polarization-dependent photocurrent in biased WSe2 EDLTs with different incidence angles.
Figure 5: Physical origin of the generation of spin-coupled valley photocurrent in WSe2 EDLTs and its electric field modulation.

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Acknowledgements

This work was supported by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under contract DE-AC02-76SF00515. B.L., H-J.Z., G.X., H.Y.H. and S-C.Z. also acknowledge FAME, one of six centres of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA. X-Q.W. and B.S. acknowledge the National Basic Research Program of China (No. 2012CB619300 and 2013CB921900) and the NSFC of China (No. 61225019, 11023003 and 61376060).

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H-T.Y., X-Q.W. and B.L. contributed equally to this work. H-T.Y., H.Y.H. and Y.C. conceived and designed the experiments. H-T.Y. performed the sample fabrication and all optical and transport measurements. H-T.Y., X-F.F., X-Q.W. and B.S. performed the CPGE measurements. B.L., H-J.Z., G.X., Y.X. and S-C.Z. performed all the DFT calculations and theoretical analyses. S-C.Z., H.Y.H. and Y.C. supervised the project. H-T.Y., B.L. and H-J.Z. wrote the manuscript, with input from all authors.

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Correspondence to Harold Y. Hwang or Yi Cui.

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Yuan, H., Wang, X., Lian, B. et al. Generation and electric control of spin–valley-coupled circular photogalvanic current in WSe2. Nature Nanotech 9, 851–857 (2014). https://doi.org/10.1038/nnano.2014.183

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