Ultrafast Evolution of the Excited-State Potential Energy Surface of TiO2 Single Crystals Induced by Carrier Cooling
Ultrafast Evolution of the Excited-State Potential Energy Surface of TiO2 Single Crystals Induced by Carrier Cooling
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DOI：
10.1103/physrevlett.110.067402
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发表时间：
2013-02-07
影响因子：
8.6
通讯作者：
Ernstorfer, Ralph
中科院分区：
文献类型：
--
作者：
Bothschafter, Elisabeth M.;Paarmann, Alexander;Ernstorfer, Ralph
我们研究了超短紫外光脉冲激发后，TiO 2中载流子冷却动力学对激发态势能面沿A（1g）光学声子坐标沿着的影响。在泵浦-探测瞬态反射率测量中观察到的大振幅相干振荡相对于纯瞬时位移激发显示出-0.2 π的相移。采用精确的密度泛函理论计算探讨了相干声子坐标的势能面最小值的动态演化，证实了共振激光激发时势能面最小值的移动，并揭示了由于激发的热电子-空穴等离子体的冷却而对位移力的显著正贡献。我们表明，这种非瞬时效应可以定量地解释实验观察到的相位使用合理的假设参数特征的激发载流子。我们的工作表明，激光激发的非平衡载流子种群的快速平衡动力学可以对晶体固体的初始结构响应有显着的影响。DOI：10.1103/PhysRevLett.110.067402
We investigate the influence of carrier cooling dynamics in TiO2 on the excited-state potential energy surface along the A(1g) optical phonon coordinate after above band-gap excitation using ultrashort ultraviolet pulses. The large amplitude coherent oscillation observed in a pump-probe transient reflectivity measurement shows a phase shift of -0.2 pi with respect to a purely instantaneous displacive excitation. The dynamic evolution of the potential energy surface minimum of the coherent phonon coordinate is explored using accurate density functional theory calculations, which confirm a shift of the potential energy surface minimum upon resonant laser excitation and reveal a significant positive contribution to the displacive force due to the cooling of the excited hot electron-hole plasma. We show that this noninstantaneous effect can quantitatively explain the experimentally observed phase using reasonable assumptions for the parameters characterizing the excited carriers. Our work demonstrates that the fast equilibration dynamics of laser-excited nonequilibrium carrier populations can have a pronounced effect on the initial structural response of crystalline solids. DOI: 10.1103/PhysRevLett.110.067402