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DF: Fachverband Dielektrische Festkörper

DF 8: Glass I

DF 8.5: Vortrag

Dienstag, 24. März 2009, 11:20–11:40, WIL B321

Investigation of the microscopic nature of tunnelling systems in glassy glycerol by using nuclear moments as local probes — •Masoomeh Bazrafshan, Celine Rüdiger, Gudrun Fickenscher, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institut für Physik, Universität Heidelberg, Germany

At low temperatures many properties of glassy materials can be described in the framework of the standard tunnelling model. It assumes the presence of 2-level systems with a broad distribution of energy splittings E, which arise from particles of mass m tunnelling between the wells of a double well potential. Up to today, the microscopic nature of these tunnelling systems, i.e. of the tunnelling particles and the tunnelling motion, is not known. We show that nuclear moments on the tunnelling particle can be used as a probe for the microscopic motion of tunnelling systems. We have performed dielectric polarisation echo experiments on a series of partially deuterated glycerol samples. The electric quadrupole moments of the deuterium nuclei interacting with local electric field gradients cause a fine splitting of the tunnelling levels, which leads to a quantum beating in small magnetic fields and a pronounced magnetic field dependence of the echo amplitude. The anisotropic interaction of the magnetic dipole moments of the hydrogen nuclei yields a similar effect on a smaller energy scale. By comparing the data to detailed numerical model calculations we were able to extract an effective tunnelling angle and can draw preliminary conclusions about the microscopic properties of the tunnelling entities.