| Issue |
Europhys. Lett.
Volume 33, Number 7, March I 1996
|
|
|---|---|---|
| Page(s) | 533 - 538 | |
| Section | Condensed matter: structure, thermal and mechanical properties | |
| DOI | https://doi.org/10.1209/epl/i1996-00374-9 | |
| Published online | 01 September 2002 | |
Cross-over to incoherent tunnelling of substitutional defects in alkali halide crystals
1
Institut Laue-Langevin - B.P. 156X, 38042 Grenoble, France
2
Institut für Angewandte Physik, Universität Heidelberg Albert-Ueberle-Str. 3-5, 69120 Heidelberg, Germany
Received:
22
September
1995
Accepted:
11
January
1996
The dielectric susceptibility of substitutional
defects in alkali halides shows a surprising
dependence on concentration c. In the dilute case
ppm, the
susceptibility is proportional to the number of
defects. It reaches a maximum at a concentration where the
average dipole-dipole interaction is equal to the bare
tunnelling amplitude of a single defect and for still
higher concentrations 
ppm it strongly decreases.
The data for various defect systems are in quantitative
agreement with a parameter-free master curve derived
from a continued fraction expansion for the relevant
correlation function. With increasing defect concentration
a universal cross-over from coherent tunnelling to
incoherent relaxation is driven by a novel relaxation mechanism,
based on the dipolar interaction.
PACS: 61.72.Yx – Interaction between different crystal defects; gettering effect / 77.22.Gm – Dielectric loss and relaxation
© EDP Sciences, 1996
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