Dark excitons and the elusive valley polarization in transition metal dichalcogenides. (1st February 2017)

• Record Type: Journal Article
• Authors: Baranowski, M; Surrente, A; Maude, D K; Ballottin, M; Mitioglu, A A; Christianen, P C M; Kung, Y C; Dumcenco, D; Kis, A; Plochocka, P
• Is Part Of: 2D materials. Volume 4:Number 2(2017)
• Publication Date: 2017-02-01
• Subjects: 2D transition metal dichalcogenides -- valley polarization -- dark excitons; Graphene -- Periodicals; Materials science -- Periodicals; Nanostructured materials -- Periodicals; 620.115
• DOI: 10.1088/2053-1583/aa58a0
• Languages: English
• ISSNs: 2053-1583

Abstract

Abstract: A rate equation model for the dark and bright excitons kinetics is proposed which explains the wide variation in the observed degree of circular polarization of the PL emission in different TMDs monolayers. Our work suggests that the dark exciton states play an important, and previously unsuspected role in determining the degree of polarization of the PL emission. A dark exciton ground state provides a robust reservoir for valley polarization, which tries to maintain a Boltzmann distribution of the bright exciton states in the same valley via the intra valley bright dark exciton scattering mechanism. The dependence of the degree of circular polarization on the detuning energy of the excitation in MoSe2 suggests that the electron–hole exchange interaction dominates over two LA phonon emission mechanism for inter valley scattering in TMDs.