Issue |
Europhys. Lett.
Volume 57, Number 3, February 2002
|
|
---|---|---|
Page(s) | 382 - 388 | |
Section | Condensed matter: structure, mechanical and thermal properties | |
DOI | https://doi.org/10.1209/epl/i2002-00472-2 | |
Published online | 01 September 2002 |
Correlation of low-energy excitations with photodarkening in
Kirchhoff-Institut für Physik der Universität Heidelberg
Albert-Ueberle-Strasse 3-5, D-69120 Heidelberg, Germany
Received:
11
June
2001
Accepted:
2
November
2001
Low-temperature sound velocity and absorption of differently
treated amorphous films have been measured around
using surface acoustic waves. The data show the
typical behaviour of glasses governed by low-energy excitations.
Illumination of the films at
using photon energies equal
to and higher than the band gap increases the absorption and
temperature dependence of the sound velocity by creation of
defects. Between
and
the change does not
depend on the wavelength but on the number of absorbed photons.
The initial state is only reset after annealing at the glass
transition temperature. The photoinduced change of the sound
velocity data suggests that upon illumination quasiharmonic
oscillators are transformed into two-level systems on average. The
strong correlation of the photoinduced changes with photodarkening
favours the twisting of adjacent
pyramids as
microscopic model for the low-energy excitations.
PACS: 62.65.+k – Acoustical properties of solids / 63.50.+x – Vibrational states in disordered systems / 78.66.Jg – Amorphous semiconductors; glasses
© EDP Sciences, 2002
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