Sound modes in composite incommensurate crystals
Abstract
We propose a simple phenomenological model describing composite crystals, constructed from two parallel sets of periodic inter-penetrating chains. In the harmonic approximation and neglecting thermal fluctuations we find the eigenmodes of the system. It is shown that at high frequencies there are two longitudinal sound modes with standard attenuation, while in the low frequency region there is one propagating sound mode and an over-damped phase mode. The crossover between these two regions is analyzed numerically and the dynamical structure factor is calculated. It is shown that the qualitative features of the experimentally observed spectra can be consistently described by our model.
- Publication:
-
European Physical Journal B
- Pub Date:
- April 2002
- DOI:
- 10.1140/epjb/e20020098
- arXiv:
- arXiv:cond-mat/0203385
- Bibcode:
- 2002EPJB...26..339C
- Keywords:
-
- PACS. 61.44.-n Semi-periodic solids – 63.20.Dj Phonon states and bands;
- normal modes;
- and phonon dispersion;
- 61.44.-n;
- 63.20.Dj;
- Semi-periodic solids;
- Phonon states and bands normal modes and phonon dispersion;
- Condensed Matter - Materials Science
- E-Print:
- 12 pages, 2 eps figures, Revtex, accepted to European Physics Journal B, (2002)