Ultrafast Carrier Thermalization and Cooling Dynamics in Few-Layer MoS2
Ultrafast Carrier Thermalization and Cooling Dynamics in Few-Layer MoS2
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DOI：
10.1021/nn504760x
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发表时间：
2014-10-01
期刊：
影响因子：
17.1
通讯作者：
Loh, Zhi-Heng
中科院分区：
文献类型：
--
作者：
Nie, Zhaogang;Long, Run;Loh, Zhi-Heng
利用10fs可见脉冲的飞秒光泵浦光探测光谱研究了少层MoS2的超快载流子动力学。在超短宽带激光脉冲光激发A和B激子跃迁后，立即观察到非热载流子分布。载流子热化在20fs内发生，并通过载流子-载流子和载流子-声子散射进行，观察到的热化时间与载流子密度和样品温度的关系证明了这一点。热化时间随载流子浓度的n(-0.37+/-0.03)标度表明，非热载流子分布的平衡是通过非马尔科夫量子动力学进行的。热费米-狄拉克载流子分布的随后冷却发生在类似于0.6ps的时间尺度上，通过载流子-声子散射。温度和通量依赖的研究揭示了热声子参与了载流子冷却过程。非绝热从头算分子动力学模拟分别预测了载流子-载流子和载流子-声子散射的时间尺度分别为40ps和0.5ps，为指定观测到的载流子动力学提供了支持。
Femtosecond optical pump-probe spectroscopy with 10 fs visible pulses is employed to elucidate the ultrafast carrier dynamics of few-layer MoS2. A nonthermal 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 nonthermal carrier distribution occurs via non-Markovian quantum kinetics. Subsequent cooling of the hot Fermi-Dirac carrier distribution occurs on the similar to 0.6 ps time scale 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 time scales of 40 fs and 0.5 ps, respectively, lend support to the assignment of the observed carrier dynamics.