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Phys Rev Lett. 2014 Jan 31;112(4):047401. Epub 2014 Jan 27.

Carrier and polarization dynamics in monolayer MoS2.

Author information

  • 1Université de Toulouse, INSA-CNRS-UPS, LPCNO, 135 Avenue de Rangueil, 31077 Toulouse, France.
  • 2Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
  • 3State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, People's Republic of China.

Abstract

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.

PMID:
24580489
[PubMed]
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