Anisotropic electron and lattice dynamics in excitonic insulator Ta2NiSe5
Anisotropic electron and lattice dynamics in excitonic insulator Ta2NiSe5
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DOI：
10.1063/5.0086701
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发表时间：
2022-05
期刊：
影响因子：
1.6
通讯作者：
Lingqiao Chu;Kai Zhang;Jin Yang;Huachao Jiang;Zhenyou Wang;F. Su
中科院分区：
文献类型：
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作者：
Lingqiao Chu;Kai Zhang;Jin Yang;Huachao Jiang;Zhenyou Wang;F. Su
利用偏振分辨飞秒光泵浦探测光谱研究了激子绝缘体Ta2NiSe5中的非平衡光生载流子动力学。电子动力学，包括热载流子冷却，激子的形成，和重组的时间尺度范围从亚皮秒到几十皮秒，已建立从瞬态反射率谱，显示出较强的面内各向异性相对于探测偏振。这种各向异性的光生载流子动力学可能是由激子极化率的晶体取向依赖性引起的。此外，我们还发现频率为1THz的相干声子的振幅受探测偏振的影响，而对泵浦偏振不敏感。这证实了相干声子的位移激发在晶格动力学中起着决定性的作用。此外，我们还发现，随着泵浦能量密度的增加，光致介电屏蔽对相干声子的振幅有抑制的趋势，表现出明显的偏振依赖性。我们的工作为激子动力学和相干声子产生的起源提供了有价值的见解，也可能有助于基于Ta2NiSe5的偏振敏感光电器件的发展。
We employ polarization-resolved femtosecond optical pump–probe spectroscopy to investigate the nonequilibrium photocarrier dynamics in excitonic insulator Ta2NiSe5. The electronic dynamics, including hot carrier cooling, exciton formation, and recombination in the timescale ranging from subpicoseconds to a few tens of picoseconds, have been established from the transient reflectivity spectra, showing strong in-plane anisotropy with respect to the probe polarization. Such anisotropic photocarrier dynamics possibly arise from the crystalline orientation dependence of the excitonic polarizability. Furthermore, we find that the amplitude of coherent phonons with a frequency of 1 THz is subject to the probe polarization, whereas it is not sensitive to the pump polarization. This substantiates that the displacive excitation of coherent phonons plays a decisive role in lattice dynamics. In addition, we find that the photo-induced dielectric screening tends to suppress the amplitude of coherent phonons with increasing pump fluence, manifesting a remarkable polarization dependence. Our work provides valuable insights into the excitonic dynamics and the origin of coherent phonon generation and also may contribute to the development of polarization-sensitive photoelectric devices based on Ta2NiSe5.