Quantum phenomena in glasses at low temperatures

Glasses exhibit surprising low-temperature properties caused by the tunneli ng motion of small atomic clusters. We report here on recent dielectric mea surements on a glass with the components BaO-Al2O3-SiO2. In contrast to exp ectation, below 100 mK the dielectric properties become sensitive to weak m agnetic fields. In this temperature range dielectric constant and dielectri c loss show an oscillatory behavior with increasing magnetic held. Below 6 mK a phase transition within the ensemble of tunneling systems is observed. (C) 2000 Published by Elsevier Science B.V. All rights reserved.