LIGHT SCATTERING FROM INCOMMENSURATE INSULATORS; MAINLY BaMnF4

摘要: The light scattering work on pyroelectric BaMnF4 is reassessed here in view of new structural information the incommensurate phase. dispersions acoustic phonon velocities Vcb and Vcc are ascribed to coupling phason amplitudon, respectively; failure observe a true soft mode Raman spectrum for T < Ti ≃ 247 K attributed overdamped nature amplitudon even 85 K; static central peak associated with symmetry breaking frozen defects; dynamic previously thought be due now assigned LA-phonon — coupling. Thus experiments have provided no direct evidence phasons or amplitudons. It suggested that Brillouin should performed ThBr4, which very simple system small damping, search predicted acoustic-phonon Finally, it demonstrated quasiperiodic superlattices provide exciting possibilities detailed comparisons between theory experiment.