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http://dx.doi.org/10.1007/s13391-018-0086-2

Effect of Phonons on Valley Depolarization in Monolayer WSe2  

Chellappan, Vijila (Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR))
Pang, Ai Lin Christina (Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR))
Sarkar, Soumya (NUS Nanoscience and Nanotechnology Initiative (NUSNNI), National University of Singapore)
Ooi, Zi En (Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR))
Goh, Kuan Eng Johnson (Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR))
Publication Information
Electronic Materials Letters / v.14, no.6, 2018 , pp. 766-773 More about this Journal
Abstract
In this paper, temperature dependence of the excitonic bands in a mechanically exfoliated tungsten diselenide ($WSe_2$) monolayer is studied using photoluminescence and circular dichroic photoluminescence (PL) in the temperature range between 8 and 300 K. The peak energies associated with the neutral exciton (A), charged exciton (trion) and localized excitons are extracted from the PL spectra revealing a trion binding energy of around 30 meV. The circular dichroic PL measured at 8 K shows about 45% valley polarisation that sharply reduces with increasing temperature to 5% at 300 K with photoexcitation energy of 1.96 eV. A detailed analysis of the emission line-width suggests that the rapid decrease of valley polarisation with the increase of temperature is caused by the strong exciton-phonon interactions which efficiently scatter the excitons into different excitonic states that are easily accessible due to the supply of excess photoexcitation energy. The emission line-width broadening with the increase of temperature indicate residual exciton dephasing lifetime < 100 fs, that correlates with the observed rapid valley depolarisation.
Keywords
Transition metal dichalcogenides; Valley polarisation; Potoluminescence; Tungsten diselenide;
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