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CAMP: Multi-particle bound-state light emission from a monolayer semiconductor

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Jun Yan, University of Massachusetts Amherst
18 September 2018 from 3:30 PM to 4:30 PM
339 Davey Laboratory
Contact Name
Jun Zhu
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Atomically-thin transition metal dichalcogenide (TMDC) semiconductors are intriguing materials hosting tightly-bound electron-hole pairs carrying quantized angular momentum, providing an appealing platform for studying exciton physics and for optically addressing the valley degree of freedom. At low temperatures in ultra-high quality WSe2 monolayers, the photoluminescence (PL) emission peaks are sharp and can arise from a variety of ground and excited states binding two, three, four or five particles. We observe PL of the 1s, 2s, 3s and 4s Rydberg series in magnetic fields up to 31 Tesla [1]. Interestingly the 2s exciton exhibits much better valley polarization and coherence than the 1s exciton [2]. We also observe PL emission from correlated quantum states of biexcitons and exciton-trions [3]. Through a set of control experiments, we determine that the biexciton consists of a spin-zero bright exciton and a spin-one dark exciton, while the exciton-trion is composed of a bright trion and a dark exciton, and that both of them are intervalley entities. Such unique spin-valley configuration gives rise to emissions with large, negative valley polarizations in contrast to that of the well-known two-particle excitons. These observations provide new opportunities for building valleytronic quantum devices harnessing a variety of excitations in the TMDC system.