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Effect of phonons on valley depolarization in monolayer WSe2
Vijila Chellappan,Ai Lin Christina Pang,Soumya Sarkar,Zi En Ooi,Kuan Eng Johnson Goh 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.6
In this paper, temperature dependence of the excitonic bands in a mechanically exfoliated tungsten diselenide (WSe 2 ) monolayeris studied using photoluminescence and circular dichroic photoluminescence (PL) in the temperature range between8 and 300 K. The peak energies associated with the neutral exciton (A), charged exciton (trion) and localized excitons areextracted from the PL spectra revealing a trion binding energy of around 30 meV. The circular dichroic PL measured at 8 Kshows about 45% valley polarisation that sharply reduces with increasing temperature to 5% at 300 K with photoexcitationenergy of 1.96 eV. A detailed analysis of the emission line-width suggests that the rapid decrease of valley polarisation withthe increase of temperature is caused by the strong exciton–phonon interactions which effi ciently scatter the excitons intodiff erent excitonic states that are easily accessible due to the supply of excess photoexcitation energy. The emission linewidthbroadening with the increase of temperature indicate residual exciton dephasing lifetime < 100 fs, that correlates withthe observed rapid valley depolarisation.