Optically initialized robust valley-polarized holes in monolayer WSe2

Wei-Ting Hsu, Yen-Lun Chen, Chang-Hsiao Chen, Pang-Shiuan Liu, Tuo-Hung Hou, Lain-Jong Li and Wen-Hao Chang ()
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Wei-Ting Hsu: National Chiao Tung University
Yen-Lun Chen: National Chiao Tung University
Chang-Hsiao Chen: Institute of Atomic and Molecular Sciences
Pang-Shiuan Liu: National Chiao Tung University
Tuo-Hung Hou: National Chiao Tung University
Lain-Jong Li: Institute of Atomic and Molecular Sciences
Wen-Hao Chang: National Chiao Tung University

Nature Communications, 2015, vol. 6, issue 1, 1-8

Abstract: Abstract A robust valley polarization is a key prerequisite for exploiting valley pseudospin to carry information in next-generation electronics and optoelectronics. Although monolayer transition metal dichalcogenides with inherent spin–valley coupling offer a unique platform to develop such valleytronic devices, the anticipated long-lived valley pseudospin has not been observed yet. Here we demonstrate that robust valley-polarized holes in monolayer WSe2 can be initialized by optical pumping. Using time-resolved Kerr rotation spectroscopy, we observe a long-lived valley polarization for positive trion with a lifetime approaching 1 ns at low temperatures, which is much longer than the trion recombination lifetime (∼10–20 ps). The long-lived valley polarization arises from the transfer of valley pseudospin from photocarriers to resident holes in a specific valley. The optically initialized valley pseudospin of holes remains robust even at room temperature, which opens up the possibility to realize room-temperature valleytronics based on transition metal dichalcogenides.

Date: 2015
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DOI: 10.1038/ncomms9963

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