Quantum behavior of coherent optical phonons

本研究对半导体和半导体中相干光学声子在高密度光激励下的量子干涉进行了实验研究。作者和他的同事在以前的研究中已经证明了半金属铋的相干对称声子的显着幅度崩塌-复苏。在本研究中，作者对铋的对称和非对称声子模以及其他半导体和半金属中的声子模进行了详细而系统的泵浦-探测实验。实验结果表明：(1)相干声子的产生并不像人们认为的那样完全由“位移激发”所支配，而是由受激拉曼过程贡献的。由于声子与电子态之间的动态量子干涉(Fano效应)，导致了振幅的崩塌-复苏。(2)通过与GaAs和Ge的比较，解释了CdTe声子振幅的亚线性功率依赖关系是由于表面的瞬时电场屏蔽饱和所致。(3)亚10ps激光脉冲激发并探测了单晶金刚石中的40 THz相干光学声子。实验结果表明，简单的泵浦-探测反射率实验为研究半导体和绝缘体固体材料中高频声子的超快动力学及其与光激载流子的相互作用提供了有力的工具。

The present study has conducted experimental investigation on quantum interference of coherent optical phonons in semiconductors and semimetals under high-density photo excitation. The author and the coworkers had shown in the previous studies a striking amplitude collapse-revival of coherent symmetric phonons of semimetal Bi. In the present study, the author have performed a detailed and systematic pump-probe experiments on the symmetric and asymmetric phonon modes of Bi, as well as on phonon modes in other semiconductors and semimetals. The obtained experimental results lead to conclude that(1)the generation of coherent phonons is not solely dominated by "Displacive Excitation", as it was considered for more than a decade, but is substantially contributed by stimulated Raman process. The amplitude collapse-revival is attributed to dynamic quantum interference between phononic and electronic states (Fano effect).(2)the sub-linear power dependence of the phonon amplitude of CdTe is explained, from comparison with GaAs and Ge, to be due to the saturation of transient electric field screening at the surface.(3)sub-10 fs laser pulses excites and probes the 40 THz coherent optical phonon in single crystal diamond. The coherent phonons are driven by electric field via resonant stimulated Raman process, without creating photo excited carriers.These results demonstrate that a simple pump-probe reflectivity experiments provide a powerful tool to investigate the ultra fast dynamics of high-frequency phonons in solid materials in semiconductors and insulators, as well as their interaction with photo-excited carriers.