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arXiv 1303.3249cond-mat.mtrl-sci
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laser激发硅的介电响应

Dielectric response of laser-excited silicon

S. A. Sato, K. Yabana, Y. Shinohara, T. Otobe, G. F. Bertsch

摘要:

利用含时密度泛函理论(TDDFT)模拟了高强度激光脉冲辐照下晶体硅的介电响应。通过求解含时的Kohn-Sham方程,将抽运场和探测场作为外场,数值模拟了抽运-探测测量。正如预期的那样,激发的硅在其响应中显示出粒子-空穴等离子体的特征。我们比较计算的响应与热模型和一个简单的Drude模型。热模型只需要一个静态的DFT计算来制备电子激发的物质,并同意相当不错的TDDFT相同的粒子空穴密度。具有两个拟合参数(电子有效质量和碰撞时间)的Drude模型在较低的激发能下也显示出相当的一致性;拟合的有效质量与载流子带色散一致。提取的德鲁德寿命范围从6 fs在弱泵浦场到低得多的值在高领域。然而,我们发现,德鲁德模型并没有得到一个很好的适合在最高领域的虚介电函数。比较热模型与Drude,我们发现提取的寿命是在相同的范围内,1-13 fs取决于温度。这些短的德鲁德寿命表明,强阻尼是可能的TDDFT,尽管没有电子散射。TDDFT响应与其他模型之间的一个显著差异在于,对探测脉冲的响应取决于泵浦脉冲的偏振。我们还发现,介电函数的虚部可以是负的,特别是对于平行极化的泵浦场和探测场。

英文摘要:

We calculate the dielectric response of crystalline silicon following irradiation by a high-intensity laser pulse, modeling the dynamics by time-dependent density functional theory (TDDFT). The pump-probe measurements are numerically simulated by solving the time-dependent Kohn-Sham equation with the pump and probe fields included as external fields. As expected, the excited silicon shows features of a particle-hole plasma in its response. We compare the calculated response with a thermal model and with a simple Drude model. The thermal model requires only a static DFT calculation to prepare electronically excited matter and agrees rather well with the TDDFT for the same particle-hole density. The Drude model with two fitted parameters (electron effective mass and collision time) also shows fair agreement at the lower excitation energies; the fitted effective masses are consistent with carrier-band dispersions. The extracted Drude lifetimes range from 6 fs at weak pumping fields to much lower values at high fields. However, we find that the Drude model does not give a good fit to the imaginary dielectric function at the highest fields. Comparing the thermal model with the Drude, we find that the extracted lifetimes are in the same range, 1-13 fs depending on the temperature. These short Drude lifetimes show that strong damping is possible in the TDDFT, despite the absence of electron scattering. One significant difference between the TDDFT response and the other models is that the response to the probe pulse depends on the polarization of the pump pulse. We also find that the imaginary part of the dielectric function can be negative, particularly for the parallel polarization of pump and probe fields.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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