Nonequilibrium dielectric behavior in glasses at low temperatures: Evidence for interacting defects

We find that recent low-temperature nonequilibrium dielectric experiments indicate that glasses have strongly interacting defects. While many of the features found in the experiments can be explained by the standard model of noninteracting two-level systems, we find that the frequency dependence cannot. Using a Monte Carlo simulation of a nearest-neighbor Ising spin glass, we show that interactions between defects can qualitatively explain the experiments because they lead to the formation of clusters and a hole in the distribution of local fields.