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 monolayers by optical spectroscopy in an out-of-plane magnetic field . In agreement with the theoretical predictions deduced from group theory analysis, magnetophotoluminescence experiments reveal a zero-field splitting between two dark exciton states. The low-energy state is strictly dipole forbidden (perfectly dark) at , while the upper state is partially coupled to light with polarization (“gray” exciton). The first determination of the dark neutral exciton lifetime in a transition metal dichalcogenide monolayer is obtained by time-resolved photoluminescence. We measure for the gray exciton state, i.e., two orders of magnitude longer than the radiative lifetime of the bright neutral exciton at .
- Received 7 August 2017
- Revised 25 September 2017
DOI:https://doi.org/10.1103/PhysRevB.96.155423
©2017 American Physical Society