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arXiv · 1708.05398

Fine Structure and Lifetime of Dark Excitons in Transition Metal Dichalcogenide Monolayers

Cedric Robert·Thierry Amand·Fabian Cadiz·Delphine Lagarde·Emmanuel Courtade·Marco Manca·Takashi Taniguchi·Kenji Watanabe·Bernhard Urbaszek·Xavier Marie
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Abstract

The intricate interplay between optically dark and bright excitons governs the light-matter interaction in transition metal dichalcogenide monolayers. We have performed a detailed investigation of the "spin-forbidden" dark excitons in WSe2 monolayers by optical spectroscopy in an out-of-plane magnetic field Bz. In agreement with the theoretical predictions deduced from group theory analysis, magneto-photoluminescence experiments reveal a zero field splitting $δ=0.6 \pm 0.1$ meV between two dark exciton states. The low energy state being strictly dipole forbidden (perfectly dark) at Bz=0 while the upper state is partially coupled to light with z polarization ("grey" exciton). The first determination of the dark neutral exciton lifetime $τ_D$ in a transition metal dichalcogenide monolayer is obtained by time-resolved photoluminescence. We measure $τ_D \sim 110 \pm 10$ ps for the grey exciton state, i.e. two orders of magnitude longer than the radiative lifetime of the bright neutral exciton at T=12 K.

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Cedric Robert, Thierry Amand, Fabian Cadiz, Delphine Lagarde, Emmanuel Courtade, Marco Manca, Takashi Taniguchi, Kenji Watanabe, Bernhard Urbaszek, Xavier Marie. 2018-05-09. Fine Structure and Lifetime of Dark Excitons in Transition Metal Dichalcogenide Monolayers. https://doi.org/10.1103/physrevb.96.155423

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