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Search: authors:"Itsuo Ohnari"

5 papers found.
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On the First-Order Structural Phase Transition of CsCuCl3-Type Cooperative Jahn-Teller System

A pseudospin-phonon coupled model with third order anharmonicity is studied within molecular field theory. The model is closely related to the one having an interaction characteristic to CsCuCl3 compounds. Some thermodynamic quantities are calculated near the first order structural phase transition point.

Central Peak and Thermal Diffusion Mode near Structural Phase Transition: Hydrodynamical Approach

The coupling of the soft mode and the thermal diffusion mode is investigated on the basis of the anharmonic soft phonon model with the aid of Mori’s hydrodynamic formula. Above the transition temperature (Tc) it is shown that a narrow central peak results from the non-linear coupling of the two modes due to the short-range order effect. We find that Enz’s result derived by the...

Short-Range Order Effects and the Central Peak in the Tunneling Model

The tunneling model is studied on the basis of the perturbation expansion using pseudo-fermion operators for spins. Effects of short-range order on its dynamical properties are investigated in the case where the perturbation expansion becomes “1/z expansion”. The effects on a pseudo-spin are taken into account in a kind of a mean field approximation for fluctuation field of the...

On the Dynamics of KDP Type Ferroelectrics. I: Formulation and Acoustic Anomaly

KDP type ferroelectrics are investigated on the basis of extended Kobayashi's model in which the proton pseudo-spin system is coupled with the acoustic phonon as well as with the optic phonon in original Kobayashi's model. A perturbational treatment is developed with the aid of the Matsubara Green's functions and a cumulant expansion. Some properties of the phase transition are...

Ground State of a Semiconductor-like System with Transverse s-d Interaction and Perturbation Method†)

Application of perturbation method to the ground state of a semiconductor-like system with transverse s-d interaction is accompanied by a serious difficulty of logarithmic divergence similar to that of the ordinary s-d problem, as the width of the forbidden band, Δ, goes to zero. As a preliminary study to improving Abrikosov approximation by considering less divergent terms, it...