Regensburg 2010 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Posters II

DY 30.13: Poster

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

Investigation of the low frequency dielectric constant of glasses at very low temperatures — •David Dähn, Michel Kinzer, Mihai Petrovici, Masoomeh Bazrafshan, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institut für Physik, Heidelberg, Germany

At temperatures below 1 K the properties of glasses are governed by atomic tunneling systems. Recently Strehlow et al. reported an unexpected magnetic field dependence of the dielectric constant of the non-magnetic glass a-BaO-Al₂O₃-SiO₂ below 5 mK. Furthermore, they observed a discontinuity of the dielectric constant at a temperature of T=5.84 mK. Later, dielectric two-pulse polarisation echo experiments revealed that nuclear quadrupole moments are responsible for the magnetic field dependence of the echo amplitude of non-magnetic glasses.

We investigated the influence of nuclear electric quadrupoles on the low frequency dielectric constant in the limit of very large quadrupole moments. A sample of the glass N-KZFS11, containing 25 mass percent of ¹⁸¹Ta₂O₃, which carries a very large quadrupole moment, was measured down to T=8 mK using an interdigital capacitor microfabricated on one surface of the planar glass sample. This type of setup combines a large capacitance with a rather small thermal mass and good thermal coupling. In addition, echo experiments were carried out on this sample which surprisingly did not show any magnetic field dependence up to B=150 mT. We discuss whether or not these observations are in conflict with present theories that include the nuclear moments in the standard tunneling model.