Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 7: Matter at Low Temperature: Poster Session
TT 7.7: Poster
Montag, 25. Februar 2008, 14:00–18:00, Poster B
Magnetic Field Dependence of Dielectric Polarization Echoes in — •Florian Klotz1, Andreas Fleischmann1, Manfred v. Schickfus1, Peter Nagel2, and Christian Enss1 — 1University of Heidelberg, Kirchhoff- Institute für Physik, Im Neuenheimer Feld 227, 69210 Heidelberg; Germany — 2IFP, Forschungszentrum Karlsruhe, PO Box 3640, 76021 Karlsruhe, Germany
Since long certain point defects in alkali halides crystals have been regarded as a model system for the tunnelling of atoms in solids. In recent measurements of the dielectric properties of non-magnetic structural glasses strong magnetic field effects have been observed. These effects are caused by atoms that are involved in tunnelling processes and carry a nuclear magnetic or quadrupolar moment. We have studied the phenomenon in dielectric two pulse polarization echo experiments on KCl crystals doped with Li. In this material the fine structure of the energy levels of the tunneling systems introduced by the nuclear moments leads to a quantum beating in echo decay measurements and to a non-monotonic dependence of the echo amplitude on magnetic fields. Since the microscopic nature of Li tunnelling centres in KCl is well known, this system can be used to compare experimental results with calculations based on a detailed microscopic model. We present the experimental data and discuss the role of nuclear magnetic moments of the KCl host material in the vicinity of tunnelling Li ions on the observed magnetic field effects.