1998 Fiscal Year Final Research Report Summary
Many-Body Effects and Photo-Induced Spatially Condensed Phases in the Exciton Systems in Layered Crystals
| Project/Area Number |
09440121
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | Osaka City University |
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Principal Investigator |
KARASAWA Tsutomu Faculty of Science, Osaka City University, Professor, 理学部, 教授 (90106336)
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| Co-Investigator(Kenkyū-buntansha) |
AKAI Ichiro Faculty of Science, Osaka City University, Lecturer, 理学部, 講師 (20212392)
KOMATSU Teruo Faculty of Science, Osaka City University, Professor, 理学部, 教授 (90047134)
IIDA Takeshi Faculty of Science, Osaka City University, Professor, 理学部, 教授 (80047191)
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| Project Period (FY) |
1997 – 1998
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| Keywords | layered crystals / high density excitons / BiI_3 / coherent collective motion of excitons / Bose-Einstain condensation / nonlinear optical response / nonlinear Schrodinger equation / 非線形Schrodinger方程式 |
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| Research Abstract |
We'v prepared good quality layered crystals BiI_3, GaSe, and PbI_2 for this project. In these crystals we have studied spatial behavior of the excitons at high density in connection with many-body effects and some new photo-induced condensed phases such as the Bose-Einstain condensation (BEC).
In BiI_3, exciton states called the stacking fault excitons (SFE) appear at a quasi two-dimensional planar defect of a stacking fault interface. The spatial behavior of SFE excited with a N_2-laser-pumped dye-laser was investigated by detecting space-resolved pump-and-probe and space-resolved photoluminescence spectra. From these spectra, there is confirmed the existence of the high density excitons moving collectively and coherently in the two-dimensional space. We examined these spectra in the picosecond time region with a mode-locked Nd : YAG laser system. It turns out that a component of the excitons expands rapidly with a velocity compared to the group velocity of the polariton mode. For this system as well as GaSe excitons, we also applied a new technique of the degenerate four-wave-mixing (DFWM) with spatially isolated two laser beams tuned at the resonant energies of the excitons. The DFWM signals was observed firstly at the middle point between the two exciting laser spots due to the propagation of the excitons. The observed extraordinary behavior of the SEE at high density is compared with the calculation based on the theory composed of a nonlinear Schrodinger equation, and the connection with the Bose-Einstain condensation of excitons is discused.
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