Dresden 2006 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 6: Solids At Low Temperature: Amorphous and Tunnel Systems, Glasses, ...

TT 6.1: Fachvortrag

Montag, 27. März 2006, 10:30–11:00, HSZ 105

Nuclear quadrupoles and magnetic-field effects in amorphous solids — •Alois Würger — CPMOH, CNRS - Université Bordeaux 1, 351 cours der la Libération, 33405 Talence, France

In recent years, the low-temperature dielectric properties of various insulating glasses (silica based materials, glycerol, mixed crystals) have been shown to depend on an applied magnetic field B [1]. The amplitude of dielectric echoes of tunnel systems oscillates with B, with a period of about 20 milliTesla, and attains the maximum value above 1 Tesla. At temperatures below 1 Kelvin, both the real and imaginary parts of the dielectric function vary with the magnetic field.

These findings are not accounted for by standard theory for diamagnetic and insulating solids. Several models have been proposed that are based on the Aharanov-Bohm phase of atoms on circular trajectories, or on nuclear spins [2]. We show that experiments clearly speak in favor of the latter, and point out the crucial role of nuclear quadrupole moments.

In particular, we discuss the magnetic-field dependence of the dielectric function. There is strong evidence that it arises from Debye relaxation.

[1] P. Strehlow et al., PRL 84, 1938 (2000); S. Ludwig et al., PRL 88, 075501 (2002); C. Enss and S. Ludwig, PRL 89, 075501 (2002); R. Haueisen and G. Weiss, Physica B 316, 555 (2004); P. Nagel et al., PRL 92, 245511 (2004);

[2] S. Kettemann, P. Fulde, P. Strehlow, PRL 83, 4325 (1999); A. Würger, PRL 88, 075502 (2002); A. Würger, A. Fleischmann, C. Enss, PRL 89, 237601 (2002)