Optical Studies of Halogen-Bridged Mixed-Valent Metal Complexes : Excitons and Nonlinear Localized Excitations

概要

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A brief review of theoretical studies on the optical properties of halogen-bridged mixed-valent metal complexes is given, with special emphasis on the following two topics. The first topic is the various optical properties of charge-transfer excitons. In order to show them, we introduce a theory of the various optical spectra which are obtained in charge-density-wave ground state. In that theory, two important effects beyond the mean-field theory are taken into account: the electron-hole correlation on the metal atoms and the classical fluctuation of the halogen-sublattice coordinates. It is found that the spectral shapes both of the linear absorption and of that in an electric field, i. e., the electroabsorption agree well with the experimental results. Moreover, the spectrum of the third-harmonic generation is also calculated by using a perturbation theory. The second topic is the intragap absorptions associated with nonlinear localized excitations which are thought to be created by light irradiation or doping. We show theoretically how the absorption spectrum is modified in the presence of a soliton or a polaron. It is clarified that the intragap absorption bands are also drasticall renormalized by the exciton effect.
理論物理学刊行会の論文
1993-10-20