Central peak dynamics of Kobayashi's model for KDP-type ferroelectrics

Peculiarities of Neutron Scattering by Order-Disorder Antiferroelectrics

“…It was supplemented by Müller's (electron-pseudospin) "field" [H z i = g l n i+l -representing the role of electron carrier density n i+l of four oxygens (index l) in CuO 2 sheet near the i-th O4] as well as by the coupling of the O4-tunnelling motion with Cu 2 -O 2 ,O 3 -vibrations (modes) of A g -or B g -symmetry (analogous to E qj+ modes) [19,21,33]. Unlike the present neutron scattering analysis, it is tempting to conclude that the well-enough refined cross sections [equations (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)] could be applied to dismiss many controversies in testing the existence of structural, dielectric and charge instabilities, asymmetry of the local Cu 2 −O4−Cu 2 potential, vibronic states, etc., up to the problem of the mutual origin of superconducting and (anti)ferroelectric phases, i.e. their possible coexistence.…”

“…More sophisticated approaches to the pseudospin-phonon dynamics utilizing the method of Green functions and of relaxational functions lead to a more complicated behavior of the modes (of their frequencies and widths). In this approach, under certain conditions (definite values of the model parameters) in the region T T c , the central peak is also reproduced with the aid of approximations being beyond the framework of random phase approximation and also by utilizing numerical calculations [7,31] (cf. [5] and references therein).…”