Ultrafast carrier thermalization and cooling dynamics in few-layer MoS₂

Nie, Zhaogang, Long, Run, Sun, Linfeng, Huang, Chung-Che, Zhang, Jun, Xiong, Qihua, Hewak, Daniel W., Shen, Zexiang, Prezhdo, Oleg V. and Loh, Zhi-Heng (2014) Ultrafast carrier thermalization and cooling dynamics in few-layer MoS₂. ACS Nano, 8 (10), 10931-10940. (doi:10.1021/nn504760x).

Abstract

Femtosecond optical pump-probe spectroscopy with 10-fs visible pulses is employed to elucidate the ultrafast carrier dynamics of few-layer MoS₂. A non-thermal carrier distribution is observed immediately following the photoexcitation of the A and B excitonic transitions by the ultrashort, broadband laser pulse. Carrier thermalization occurs within 20 fs and proceeds via both carrier-carrier and carrier-phonon scattering, as evidenced by the observed dependence of the thermalization time on the carrier density and the sample temperature. The n-0.37±0.03-scaling of the thermalization time with carrier density suggests that equilibration of the non-thermal carrier distribution occurs via non-Markovian quantum kinetics. Subsequent cooling of the hot Fermi-Dirac carrier distribution occurs on the ~0.6-ps timescale via carrier-phonon scattering. Temperature- and fluence-dependence studies reveal the involvement of hot phonons in the carrier cooling process. Nonadiabatic ab initio molecular dynamics simulations, which predict carrier-carrier and carrier-phonon scattering timescales of 40 fs and 0.5 ps, respectively, lend support to the assignment of the observed carrier dynamics

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Contributors

Author: Chung-Che Huang

Author: Daniel W. Hewak

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