Regensburg 2010 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Posters II

DY 30.15: Poster

Donnerstag, 25. März 2010, 16:00–18:00, Poster C

What can nuclear magnetic moments reveal about the microscopic nature of tunnelling systems in glasses? — •Masoomeh Bazrafshan, Gudrun Fickenscher, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institut Für Physik, Heidelberg

More than thirty years ago anomalies in glasses at low temperatures were successfully explained by introducing atomic tunnelling systems (TS), described by the phenomenological standard tunnelling model. However, the universal behaviour of glasses prevented the experimental investigation of the microscopic nature of these TSs. Recently, unexpected magnetic field effects of the dielectric constant and of the two pulse polarisation echo amplitude, observed in non-magnetic glasses, turned out to be a proper experimental tool to investigate the microscopics of TSs. The echo experiments, done on glycerol and deuterated glycerol, prove that the interaction of nuclear quadrupole moments with local electric field gradients as well as interacting nuclear magnetic dipoles cause the observed magnetic field effects. Interestingly, the magnitude of the echo amplitude variations in magnetic fields is governed by the motion of the TSs. We present the measured effects together with numerical calculations based on the mentioned interactions which enable us to derive details of the TS's microscopic motions in glycerol. These calculations were done without considering dissipative processes acting at finite temperatures and, therefore, are strictly valid only at T=0. An analysis of the measured echo decay at different temperatures suggests that this quantum behaviour is observed, on the time scale of our measurements, at temperatures below 5mK.