The paraelectric low-frequency dynamics of KH2PO4-type crystals has been investigated on the basis of a new time-dependent pseudospin Hamiltonian which includes both long-range electrostatic interactions and strong short-range interactions which exist within clusters of four neighbouring bonds. The static limit of this model is the well-known four-particle cluster tunnelling Hamiltonian which gives a good account of the static properties of the first-order phase transition in these crystals. First-order time-dependent perturbation theory is used to calculate the dynamical linear response of the system.
Low-Frequency Dynamics of KH2PO4 Type Crystals
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