Anomalous behavior of ε(ω) in glasses at low temperature due to bias application

Abstract

We report new evidence for the importance of interactions between tunneling two level systems in the ac dielectric response of glasses at very low temperatures (500μK to 150mK). After the application of a large dc electric field we observed logarithmic relaxations in ∈′(ω) and ∈″(ω) for up to 10⁴ s. The frequency dependence of the relaxation in ∈′(ω) observed previously at higher temperatures vanishes for temperatures well below the minimum of ∈′(ω,T), in agreement with a model incorporating 1/r ³ interactions to the density of states of the two level systems. We also see a feature in fast continuous bias sweeps supporting the coexistence of responses due to an interaction-modified density of states and a change in level population.