Evidence of anomalous dispersion of the generalized sound velocity in glasses

Details Evidence of anomalous dispersion of the generalized sound velocity in glasses Evidence of anomalous dispersion of the generalized sound velocity in glasses

2004-02-05

arxiv.org/abs/cond-mat/0402161v1

Physics

Condensed Matter

Disordered Systems and Neural Networks

5 pages, 3 figures. To appear in Phys. Rev. B

Scientific paper

10.1103/PhysRevB.69.100201

The dynamic structure factor, S(Q,w), of vitreous silica, has been measured by inelastic X-ray scattering in the exchanged wavevector (Q) region Q=4-16.5 nm-1 and up to energies hw=115 meV in the Stokes side. The unprecedented statistical accuracy in such an extended energy range allows to accurately determine the longitudinal current spectra, and the energies of the vibrational excitations. The simultaneous observation of two excitations in the acoustic region, and the persistence of propagating sound waves up to Q values comparable with the (pseudo-)Brillouin zone edge, allow to observe a positive dispersion in the generalized sound velocity that, around Q=5 nm-1, varies from 6500 to 9000 m/s: this phenomenon was never experimentally observed in a glass.

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