The dynamics of KD2PO4 along the transverse x direction is investigated using a pseudospin model which takes into account the transverse dipole moments of the hydrogen bonds and incorporates both short-range and long-range interaction effects. A four-cluster approximation to the Glauber equations of motion for the E-mode pseudospin fluctuations is employed. It is found that these fluctuations have three different relaxation times below Tc and two above Tc However, in the low-frequency region the dynamical susceptibility has a Debye-type frequency dependence with one relaxation time τx. The temperature dependence of τx is calculated within the present model and is compared to that derived from the randomphase approximation (RPA). It is found that the relation between τx and the static transverse susceptibility χx is markedly different from the RPA result τx~Tχx. The present theory explains in a consistent way the available experimental data on the dynamical properties of KD2PO4 in both the longitudinal and transverse directions.
Effect of Short-Range Interactions on the Transverse Dynamical Properties of KD2PO4
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