硅中观察到的超快非对称类Rosen-Zener相干声子响应
Ultrafast asymmetric Rosen-Zener-like coherent phonon responses observed in silicon
摘要：
我们研究了非掺杂硅晶体中相干声子产生的时间信号的光谱轮廓。本文采用作者[Y. Watanabe等人，Phys. Rev. B 95，014301（2017）;同上，96，125204（2017）]。的光谱不对称性揭示在频域的信号的条件下，LO声子模式保持几乎大力共振与等离子体激元模式在早期的时间区域，这持续约100 fs后立即照射的超短泵浦激光脉冲。应当理解，基于绝热时间图，这种不对称性是由两种模式之间的Rosen-Zener耦合引起的。通过测量随时间变化的电光反射率信号，得到了相关的实验结果，并证明了这些与计算结果是一致的。随着光激发载流子密度从满足上述条件的载流子密度进一步向载流子密度的较高侧和较低侧变化，光谱变得更加对称。此外，对CP信号的载流子密度的光章动的效果进行了解决，目前的结果进行了比较，由瞬态Fano共振所造成的不对称性，并在文中的GaAs晶体中观察到的光谱轮廓。
英文摘要：
We investigate the spectral profiles of time signals attributed to coherent phonon generation in an undoped Si crystal. Here, the retarded longitudinal-optical (LO) phonon Green function relevant to the temporal variance of induced charge density of ionic cores is calculated by employing the polaronic quasiparticle model developed by the authors [Y. Watanabe et al., Phys. Rev. B 95, 014301 (2017); ibid., 96, 125204 (2017)]. The spectral asymmetry is revealed in the frequency domain of the signals under the condition that an LO phonon mode stays almost energetically resonant with a plasmon mode in the early time region; this lasts for approximately 100 fs immediately after the irradiation of an ultrashort pump-laser pulse. It is understood that based on the adiabatic picture in time, this asymmetry is caused by the Rosen-Zener coupling between both modes. The associated experimental results are obtained by measuring time-dependent electro-optic reflectivity signals, and it is proved that these are in harmony with the calculated ones. The spectra become more symmetric, as the photoexcited carrier density further changes from that meeting the above condition to higher and lower sides of carrier densities. Moreover, the effect of optical nutation of carrier density on the CP signals is addressed, and the present results are compared with the asymmetry caused by transient Fano resonance, and the spectral profiles observed in a GaAs crystal in the text.
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