Connection between fast and slow dynamics in glass-forming systems.
Capaccioli S., Paciaroni A., Ciampalini G., Leporini D., Pachetti M., Valenti S., Ngai K.L.
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We report recent studies by neutron scattering and THz absorption on the fast dynamics (typically in the ns-ps range) of different classes of glass formers. In the glassy state the molecular caged dynamics ($i.e.$ libration-vibration motions) appear in susceptibility losses as a frequency power law with a small exponent, before attaining the region where a microscopic peak dominates the vibrational density of states. Remarkably, the fast caged dynamics amplitude appears strongly linked to slow dynamics, such as alpha- and beta-relaxation revealed by calorimetry or dielectric spectroscopy. This study sheds light on the interplay between fast and slow dynamics in glasses.