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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.
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.