Terahertz emission spectroscopy of ultrafast exciton shift current in the noncentrosymmetric semiconductor CdS
Terahertz emission spectroscopy of ultrafast exciton shift current in the noncentrosymmetric semiconductor CdS
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DOI：
10.1103/physrevb.103.l241111
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发表时间：
2021-06
影响因子：
3.7
通讯作者：
M. Sotome;M. Nakamura;T. Morimoto;Y. Zhang;G. Guo;M. Kawasaki;N. Nagaosa;Y. Tokura;N. Ogawa
中科院分区：
文献类型：
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作者：
M. Sotome;M. Nakamura;T. Morimoto;Y. Zhang;G. Guo;M. Kawasaki;N. Nagaosa;Y. Tokura;N. Ogawa
由于电子能带的几何贝里相，如果晶体中的反转对称性被打破，预计电荷中性激子将携带真正的光电流。我们利用太赫兹发射光谱检测了典型极性半导体CdS中的激子位移电流。在激子共振能量处，光电流谱中出现了一个明显的峰值，这是由于激子内部的电子和空穴在实际空间中发生了明显的位移，从而在亚皮秒时间尺度上产生有限的瞬态电荷电流。我们的研究结果阐明了电荷中性光激发的贝里相物理，并揭示了通过激子产生的新型能量收集机制。
The charge-neutral exciton has been predicted to carry genuine photocurrent due to the geometric Berry phase of the electronic bands, if the inversion symmetry in a crystal is broken. We detect such exciton shift current in a prototypical polar semiconductor CdS by using terahertz emission spectroscopy. A distinct peak emerges in the photocurrent spectra at the energy of the exciton resonance, which is demonstrated to result from the distinct displacements of electrons and holes in real space within the excitons to produce a finite transient charge current at subpicosecond time scale. Our findings elucidate the Berry phase physics of the charge-neutral photoexcitations and also shed light on the novel energy harvesting mechanism by exciton generation.