2019/06/30 by Erfu Liu, Jeremiah van Baren, Takashi Taniguchi +3 · 1 citation
Physics and Astronomy · #cond-mat.mes-hall
paper · pdf · doi:10.1103/physrevresearch.1.032007
published as Phys. Rev. Research 1, 032007 (2019) · 37 pages, 5 figures
arxiv created 2019/10/25 · arxiv updated 2019/10/30
We observe a set of three replica luminescent peaks at ~21.4 meV below the dark exciton, negative and positive dark trions (or exciton-polarons) in monolayer WSe2. The replica redshift energy matches the energy of the zone-center E"-mode optical phonons. The phonon replicas exhibit parallel gate dependence and same g-factors as the dark excitonic states, but follow the valley selection rules of the bright excitonic states. While the dark states exhibit out-of-plane transition dipole and valley-independent linearly polarized emission in the in-plane directions, their phonon replicas exhibit in-plane transition dipole and valley-dependent circularly polarized emission in the out-of-plane directions. Our results and symmetry analysis show that the K-valley dark exciton decays into a left-handed chiral phonon and a right-handed photon, whereas the K'-valley dark exciton decays into a right-handed chiral phonon and a left-handed photon. Such valley selection rules of chiral phonon replicas can be utilized to identify the valleys of the dark excitonic states and explore their chiral interactions with phonons.