Dynamic central peaks in solids: Progress and prospects

The dynamics of order parameter fluctuations in the near vicinity of solid state phase transitions have been vigorously studied both theoretically and experimentally for the past decade. Very near Tc, inelastic scattering spectra typically exhibit singular low frequency behavior (i.e. central peaks) suggesting complicated order parameter dynamics. This paper illustrates the use of high contrast, high resolution light scattering to elucidate various microscopic mechanisms for such behavior in three cases: (1) two phonon difference processes in structural transitions; (2) coupled electron-phonon dynamics in cooperative Jahn Teller systems; and (3) magnetic energy density fluctuations in antiferromagnetic KNiF3.