Europhys. Lett.
Volume 47, Number 1, July 1999
Page(s) 56 - 62
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 September 2002
DOI: 10.1209/epl/i1999-00351-x

Europhys. Lett, 47 (1), pp. 56-62 (1999)

The Raman coupling function in amorphous silica and the nature of the long-wavelength excitations in disordered systems

A. Fontana 1, R. Dell'Anna 1, M. Montagna 1, F. Rossi 1, G. Viliani 1
G. Ruocco 2, M. Sampoli 3, U. Buchenau 4 and A. Wischnewski 4

1 Università di Trento and Istituto Nazionale di Fisica della Materia
I-38050, Povo, Trento, Italy
2 Università de L'Aquila and Istituto Nazionale di Fisica della Materia
I-67100, L'Aquila, Italy
3 Università di Firenze and Istituto Nazionale di Fisica della Materia
I-50139, Firenze, Italy
4 Institut für Festkörperforschung, Forschungszentrum Jülich
Postfach 1913, D-52425, Jülich, Germany

(received 21 October 1998; accepted in final form 21 April 1999)

PACS. 63.50${\rm +x}$ - Vibrational states in disordered systems.
PACS. 61.43Fs - Glasses.


New Raman and incoherent neutron scattering data at various temperatures and molecular-dynamic simulations in amorphous silica are compared to obtain the Raman coupling coefficient $C(\omega)$and, in particular, its low-frequency limit. This study indicates that in the $\omega \rightarrow 0$limit $C(\omega)$ extrapolates to a nonvanishing value, giving important indications on the characteristics of the vibrational modes in disordered materials; in particular our results indicate that even in the limit of very long wavelength the local disorder implies nonregular local atomic displacements.


Copyright EDP Sciences