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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 17: Glasses II (joint session DY/DF/CPP)
CPP 17.11: Talk
Tuesday, March 12, 2013, 12:15–12:30, H46
Interaction between tunnelling systems in glasses — •Gudrun Fickenscher1, Christian Schötz1, Paul Faßl1, Alexander Archer1, Alexander Burin2, Manfred von Schickfus1, Andreas Fleischmann1, and Christian Enss1 — 1Kirchhoff-Institut für Physik, Universität Heidelberg — 2Tulane 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.