Some remarks on the low-energy excitations in glasses: interpretation of Boson peak data

Abstract

The frequency-reduced representation, g(ω)/ω², of the vibrational density of states g(ω), known as the Boson peak is frequently used to extract information on structural and dynamical properties of glasses and supercooled liquids. The g(ω)/ω² representation is preferred over the true excess of the vibrational modes, defined as the difference between the total g(ω) and the Debye contribution, for practical reasons. Analysis of a large body of the available experimental data from inelastic neutron and Raman scattering reveals that reduction procedures distort to a great extent the otherwise symmetric excess density of states. The frequency and the intensity of the Boson peak are very sensitive to minor modifications of the distribution of the excess. The quantitative use of the g(ω)/ω² function leads to some peculiar results that contradict our general perception about structure and dynamics of glass-forming materials. We stress that the physics of the low-energy excitations are hidden in the excess density of states, which should attract more attention both from the experimental as well as the theoretical point of view.

Acknowledgements

S. N. Yannopoulos acknowledges financial support from the General Secretariat for Research and Technology – Hellas in the framework of the program PENED 2003 (03EΔ887). The Hellenic Telecommunications Organization (OTE S.A.) is also thanked for support.