Abstract
As hosts for tightly-bound electron-hole pairs carrying quantized angular momentum, atomically-thin semiconductors of transition metal dichalcogenides (TMDCs) provide an appealing platform for optically addressing the valley degree of freedom. In particular, the valleytronic properties of neutral and charged excitons in these systems have been widely investigated. Meanwhile, correlated quantum states involving more particles are still elusive and controversial despite recent efforts. Here, we present experimental evidence for four-particle biexcitons and five-particle exciton-trions in high-quality monolayer tungsten diselenide. Through charge doping, thermal activation, and magnetic-field tuning measurements, we determine that the biexciton and the exciton-trion are bound with respect to the bright exciton and the trion, respectively. Further, both the biexciton and the exciton-trion are intervalley complexes involving dark excitons, giving rise to emissions with large, negative valley polarization in contrast to that of the two-particle excitons. Our studies provide opportunities for building valleytronic quantum devices harnessing high-order TMDC excitations.
Highlights
As hosts for tightly-bound electron-hole pairs carrying quantized angular momentum, atomically-thin semiconductors of transition metal dichalcogenides (TMDCs) provide an appealing platform for optically addressing the valley degree of freedom
We report the experimental observation of optical features due to biexcitons confined to a two-dimensional (2D) semiconductor, the monolayer (1L) tungsten diselenide (WSe2), a type of transition metal dichalcogenide (TMDC)
Our findings shed light on many-body physics of transition metal dichalcogenides, and pave way for developing valleytronic devices and spinvalley entangled photon sources based on TMDCs
Summary
As hosts for tightly-bound electron-hole pairs carrying quantized angular momentum, atomically-thin semiconductors of transition metal dichalcogenides (TMDCs) provide an appealing platform for optically addressing the valley degree of freedom. Thermal activation, and magnetic-field tuning measurements, we determine that the biexciton and the exciton-trion are bound with respect to the bright exciton and the trion, respectively Both the biexciton and the exciton-trion are intervalley complexes involving dark excitons, giving rise to emissions with large, negative valley polarization in contrast to that of the two-particle excitons. As a result of their unique spin and valley configurations, both the biexciton and the exciton-trion produce emissions with valley polarization that has an opposite sign compared to the well-known bright exciton in a magnetic field[9,10], and the degree of the valley polarization is much larger As such, these multi-particle states are distinct from four-wave-mixing (FWM) measurements on MoSe2 and WSe2 in which the neutral and charged biexcitons do not involve the dark exciton[4,11]. Our findings shed light on many-body physics of transition metal dichalcogenides, and pave way for developing valleytronic devices and spinvalley entangled photon sources based on TMDCs
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