Photoinduced Phase Transitions and their Dynamics

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We studied mainly following three subjects :1) Monte-Carlo simulation Study on domain formation in photo-induced transition : [Fe(2-pic)_3]Cl_3EtOH shows cooperative low-spin (LS) to high-spin (HS) states transition when the light is irradiated to the LS phase. We studied theoretically these phenomena by Monte Carlo and the analytic methods. It was shown that the fluctuation due to the repetition of the excitation by light and de-excitation process acts as the driving force to surmount the barrier of domain nucleation. To explain the macroscopic phase separation, a model including the coupling with volume striction mode was introduced. The sharp step-like conversion was ascribed to the de-pinning effect of the volume striction.2) Magnetic semiconductors : The ferromagnetism induced by the low density carrier which is doped by optical or chemical methods was studied by both Monte Carlo and the analytic methods. The role of magnetic polaron effect in the magnetism and the optical process was analyzed.3) Electronic band structure of Kco[Fe(CN)_6][16] : To clarify the electronic structures of the photo-induced ferrimagnetic state, the LDA band calculations on the basis of the FLAPW method was carried out. The energy of Co-d γ band decreases and locates very near the Fermi energy, and thus electron transfers from Fe ion site state to Co site in the excited state.