Non-linear Optical Responses and Many-Body Effects of Excitonic Fano Resonance States

本研究旨在从理论上理解静电场作用下半导体超晶格的非线性光学响应和多体效应，称之为Wannier-Stark梯形(WSL)。特别注意了半导体的低维对激子Fano共振(FR)态的两种影响。主要研究结果列举如下：(1)基于多通道散射理论，模拟了强静电场作用下WSL-FR态的齐纳效应。在产生齐纳共振的特定电场下，观察到载流子(电子或空穴)的子带能量与相关波函数的明显离域之间的强烈反交叉。这导致激子光谱作为函数…的强调制离子的电场强度越大。简并四波混频(DFWM)光谱中修饰激子FR态的不对称双重态分裂从半导体Bloch方程出发，考虑到多体效应，研究了强抽运脉冲激光和相对弱探测脉冲激光照射在简并四波混频(DFWM)靶上的DFWM信号。在光谱分辨的DFWM谱中观察到了由普通激子束缚态引起的对称双重态分裂，称为Autler-Townes分裂。另一方面，当激子FR态被特别考虑时，发现由于微观偏振相干性和FR波函数与反映Fano-Q值大小程度的位相的干扰，光谱变得不对称。这种新型双重态的形状和能量位置很大程度上取决于多体效应和抽运光的强度。(3)动态WSL的AC-Zener效应将WSL与具有周期重复频率的THz激光强耦合的系统称为动态WSL。众所周知，利用单色激光器可以相干地控制DWSL的Floquit态。通过计算相关Floquit态的准能和吸收光谱，研究了周期脉冲串驱动的DWSL的交流齐纳效应。发现了量子控制的新可能性，即当脉冲波形为正方形或锯齿形时，可以相干地消除DWSL的AC-Zener效应。另一方面，对于具有其他波形的周期脉冲串，发现随着激光强度的增加，出现了反常的负吸收。较少

The present research project is aimed at the theoretical understanding of the non-linear optical response and the many-body effect on semiconductor superlattices with a static electric field along the direction of the crystal growth, termed the Wannier Stark ladder (WSL). In particular, an attention is paid to such two effects on excitonic Fano resonance (FR) states ascribable to the low dimensionality of the semiconductor concerned. The main research results are enumerated in the following :(1) Zener effects on WSL-FR states under an intense static electric fieldPhotoabsorption spectra of an exciton of this system are simulated based on the multi-channel scattering theory. The strong anticrossing between the subband energies of a carrier (an electron or a hole) and the conspicuous delocalization of the associated wavefunctions are observed under the particular applied electric field giving rise to the Zener resonance. This results in strong modulation of the exciton spectra as a funct … More ion of strength of the electric field. To put it concretely, the red shift of the absorption edge and the irregular variation of the FR profile are found.(2) Asymmetric doublet splitting of the dressed exciton FR state in the degenerate four-wave mixing (DFWM) spectroscopyBased on the semiconductor Bloch equations in view of the many-body effect, the DFWM signals of the WSL are examined, where both strong pump pulse laser and relatively weak probe pulse laser are irradiated on this target. It is known that the symmetric doublet splitting attributed to an ordinary exciton bound state is observed in the spectrally-resolved DFWM spectra, which is termed the Autler-Townes splitting. On the other hand, when the exciton FR state is particularly concerned, it is found that the spectra become asymmetric, resulting from the interference of the microscopic polarization coherence and the FR wave function with the phase reflecting the degree of the magnitude of the Fano-q value. The profile and the energy position of the novel doublet greatly depend on the many-body effect as well as the intensity of the pump light.(3) ac-Zener effect of the dynamic WSL (DWSL)The system of the WSL strongly coupled with a THz laser with periodic repetition is termed the DWSL. It is well known that the Floquet state of the DWSL can be coherently controlled by means of a monochromatic laser. Here, the ac-Zener effect on the DWSL driven by a periodic pulse train is examined by calculating the quasienergies and the absorption spectra of the associated Floquet states. The novel possibility of the quantum control is found that the ac-Zener effect of the DWSL can be coherently removed when the wave form of the pulse is of the either square or saw-toothed shape. On the other hand, as regards the periodic pulse train with other wave forms, it is found that anomalous negative absorption manifest itself with increasing the intensity of the laser concerned. Less