title: Optically initialized robust valley-polarized holes in monolayer WSe2.
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.
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.
authors.forename: Wei-Ting
authors.initials: WT
authors.lastname: Hsu
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.
authors.forename: Yen-Lun
authors.initials: YL
authors.lastname: Chen
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Chang-Hsiao
authors.initials: CH
authors.lastname: Chen
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.|Department of Automatic Control Engineering, Feng Chia University, Taichung 40724, Taiwan.
authors.forename: Chiang-Hsiao
authors.initials: CH
authors.lastname: Chen
authors.affiliation: Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 30010, Taiwan.
authors.forename: Pang-Shiuan
authors.initials: PS
authors.lastname: Liu
authors.affiliation: Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 30010, Taiwan.|Taiwan Consortium of Emergent Crystalline Materials (TCECM), Ministry of Science and Technology, Taipei 10622, Taiwan.
authors.forename: Tuo-Hung
authors.initials: TH
authors.lastname: Hou
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.|Taiwan Consortium of Emergent Crystalline Materials (TCECM), Ministry of Science and Technology, Taipei 10622, Taiwan.|Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Lain-Jong
authors.initials: LJ
authors.lastname: Li
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu 30010, Taiwan.|Taiwan Consortium of Emergent Crystalline Materials (TCECM), Ministry of Science and Technology, Taipei 10622, Taiwan.
authors.forename: Wen-Hao
authors.identifier: http://orcid.org/0000-0003-4880-6006
authors.initials: WH
authors.lastname: Chang