Volume 83, Number 5, September 2008
Article Number 56004
Number of page(s) 5
Section Condensed Matter: Structural, Mechanical and Thermal Properties
Published online 01 September 2008
EPL, 83 (2008) 56004
DOI: 10.1209/0295-5075/83/56004

Scattering of phonons on two-level systems in disordered crystals

D.-V. Anghel1 and D. Churochkin2, 3

1   Department of Theoretical Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH) - 407 Atomistilor, Magurele-Bucharest 077125, Romania, EU
2   Saratov State University - 410012, Astrakhanskaya St. 83, Saratov, Russia
3   R & D Institute “Volga” - Saratov 410052, Russia

received 9 April 2008; accepted in final form 10 July 2008; published September 2008
published online 1 September 2008

We calculate the scattering rates of phonons on two-level systems in disordered trigonal and hexagonal crystals. We apply a model in which the two-level system, characterized by a direction in space, is coupled to the strain field of the phonon via a tensor of coupling constants. The structure of the tensor of coupling constants is similar to the structure of the tensor of elastic stiffness constants, in the sense that they are determined by the same symmetry transformations. In this way, we emphasize the anisotropy of the interaction of elastic waves with the ensemble of two-level systems in disordered crystals. We also point to the fact that the ratio $\gamma _{l}/\gamma _{t}$ has a much broader range of allowed values in disordered crystals than in isotropic solids.

61.43.-j - Disordered solids.
62.40.+i - Anelasticity, internal friction, stress relaxation, and mechanical resonances. - Phonon-defect interactions.

© EPLA 2008