At temperatures below 1 K, the capacitance of a glass sample changes due to the application of a dc field in accordance with Burin’s dipole gap theory [J. Low Temp. Phys. 100, 309 (1995)]. However, we now report that below 20 mK, during the first sweep cycle of the dc electric field, the capacitance is smaller by about ${10}^{-5}$ compared to any subsequent sweep. Despite this overall shift, the field dependence follows the dipole gap predictions. In a subsequent sweep to higher dc fields the dielectric constant drops by about ${10}^{-5}$ as soon as the applied field is higher than any field previously applied. A picture involving the dynamics of resonant pairs provides a qualitative description of this behavior.

• Received 11 January 2003

DOI:https://doi.org/10.1103/PhysRevLett.90.195501