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Generation, transport and detection of valley-locked spin photocurrent in WSe2–graphene–Bi2Se3 heterostructures

Abstract

Quantum optoelectronic devices capable of isolating a target degree of freedom (DoF) from other DoFs have allowed for new applications in modern information technology. Many works on solid-state spintronics have focused on methods to disentangle the spin DoF from the charge DoF1, yet many related issues remain unresolved. Although the recent advent of atomically thin transition metal dichalcogenides (TMDs) has enabled the use of valley pseudospin as an alternative DoF2,3, it is nontrivial to separate the spin DoF from the valley DoF since the time-reversal valley DoF is intrinsically locked with the spin DoF4. Here, we demonstrate lateral TMD–graphene–topological insulator hetero-devices with the possibility of such a DoF-selective measurement. We generate the valley-locked spin DoF via a circular photogalvanic effect in an electric-double-layer WSe2 transistor. The valley-locked spin photocarriers then diffuse in a submicrometre-long graphene layer, and the spin DoF is measured separately in the topological insulator via non-local electrical detection using the characteristic spin–momentum locking. Operating at room temperature, our integrated devices exhibit a non-local spin polarization degree of higher than 0.5, providing the potential for coupled opto-spin–valleytronic applications that independently exploit the valley and spin DoFs.

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Fig. 1: Proposed device scheme and electrical characterization of WSe2–graphene–TI heterostructures
Fig. 2: Light-helicity-dependent local photocurrent response of WSe2 and Bi2Se3.
Fig. 3: Non-local CPGE measurements and gate-dependent local/non-local polarizability.

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Acknowledgements

This work was supported by Samsung Research Funding Centre of Samsung Electronics under project number SRFC-MA1402-02.

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S.C. and M.N. contributed equally to this work. H.C. conceived the main idea and designed the experimental protocols. S.C., M.N., J.-H.K., J.S., H.B., D.L., H.S., S.Y., S.L., W.S., C.-H.L., M.-H.J. and D.K. performed the sample fabrication. S.C., S.S., M.N. and J.L. performed the CPGE measurements. H.K. and J.K. provided single crystal Bi2Se3. H.C. supervised the project. S.C., M.N. and H.C. wrote the manuscript with input from all authors.

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Correspondence to Hyunyong Choi.

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Supplementary Figures 1–6, Supplementary Tables 1–3, Supplementary References

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Cha, S., Noh, M., Kim, J. et al. Generation, transport and detection of valley-locked spin photocurrent in WSe2–graphene–Bi2Se3 heterostructures. Nature Nanotech 13, 910–914 (2018). https://doi.org/10.1038/s41565-018-0195-y

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