Transverse Susceptibility and E-mode Raman Spectra of a KH₂PO₄ Crystal

Abstract

Low frequency E(x, y)-mode Raman spectrum of a KH₂PO₄ crystal is discussed in terms of the pseudo-spin model extended by Havlin et al. to the problem of transverse susceptibility. Temperature dependence of the susceptibility obtained from the integrated intensity of a broad continuum of the Raman spectrum can be well interpreted by their theory. The theory indicates that this mode, just like the B₂(z)-soft phonon mode, originates from a zone-center phonon corresponding to a collective proton motion in the a-b plane. Dynamics of the E-mode is also discussed in the framework of the pseudo-spin formalism and it is shown that this model is applicable not only to B₂(z) soft mode but also, at least qualitatively, to the E(x, y) mode in spite of the apparently different behaviour of the two modes with respest to the phase transition.