Collective Low-Frequency Excitations in a Molecular Glass

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Abstract
The excitations below 40 meV of a glass-former mixture (CD3OD 6% D2O) have been studied by neutron spectroscopy. A well-resolved inelastic peak with a dispersion behaviour reminiscent of those found in metallic glasses has been observed for temperatures above 10 K. The presence of such peak is correlated with an abrupt enhancement of the total vibrational density of states (TDOS). The nature of the excitations is analysed by means of their wave vector dependence. Finally, the TDOS are tentatively interpreted in terms of a coupling between sound waves and localized excitations, which becomes effective for temperatures above 10 K.