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

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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