# Regensburg 2013 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 10: Glasses (joint session DY/DF/CPP)

### DY 10.11: Vortrag

### Dienstag, 12. März 2013, 12:15–12:30, H46

**Interaction between tunnelling systems in glasses** — •Gudrun Fickenscher^{1}, Christian Schötz^{1}, Paul Faßl^{1}, Alexander Archer^{1}, Alexander Burin^{2}, Manfred von Schickfus^{1}, Andreas Fleischmann^{1}, and Christian Enss^{1} — ^{1}Kirchhoff-Institut für Physik, Universität Heidelberg — ^{2}Tulane University, New Orleans, USA

The low-temperature properties of glasses are governed by tunnelling systems as described in the well-established standard tunnelling model. Interactions between tunnelling systems and phonons lead to energy relaxation. In addition, the interaction between individual tunnelling systems, as predicted by spectral diffusion theory, causes phase decoherence phenomena. To study these interaction processes we have measured the decay of different types of polarization echoes in the standard glass BK7 with respect to the delay time at temperatures between 7.5mK and 70mK. The decay of 2- and 3-pulse echoes is strongly influenced by spectral diffusion. In the case of 3-pulse echoes we expect, in addition, a significant contribution to the decay by energy relaxation processes. On comparing the measured data to numerical calculations we find that the decay of the echo amplitude is slower than predicted by the standard theory at all temperatures. This leads us to the assumption, that there exists a small subspace of tunnelling systems which interact very little with phonons due to a very small coupling constant. Including this subspace in the calculations we can accurately fit the data for all echo types and temperatures with one consistent set of parameters.