Carrier and Polarization Dynamics in Monolayer MoS 2

• Published in: Physical review letters 2014-01, Vol.112 (4), Article 047401
• Main Authors: Lagarde, D., Bouet, L., Marie, X., Zhu, C. R., Liu, B. L., Amand, T., Tan, P. H., Urbaszek, B.
• Format: Article
• Language: English
• Subjects: Optics; Physics
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.112.047401

In monolayer MoS2, optical transitions across the direct band gap are governed by chiral selection rules, allowing optical valley initialization. In time-resolved photoluminescence (PL) experiments, we find that both the polarization and emission dynamics do not change from 4 to 300 K within our time resolution. We measure a high polarization and show that under pulsed excitation the emission polarization significantly decreases with increasing laser power. We find a fast exciton emission decay time on the order of 4 ps. The absence of a clear PL polarization decay within our time resolution suggests that the initially injected polarization dominates the steady-state PL polarization. The observed decrease of the initial polarization with increasing pump photon energy hints at a possible ultrafast intervalley relaxation beyond the experimental ps time resolution. By compensating the temperature-induced change in band gap energy with the excitation laser energy, an emission polarization of 40% is recovered at 300 K, close to the maximum emission polarization for this sample at 4 K.