Nonequilibrium and hysteretic low temperature dielectric response to strain in glasses

We present data on the nonequilibrium ac dielectric response of amorphous insulators to the application of a quasi-dc mechanical strain field below 150 mK. The behavior of the system after perturbation by a strain field is analogous to that observed after the application of a dc electrical field. In the current theoretical framework the nonequilibrium response is due to a time dependent density of states correction resulting from TLS-TLS interactions. In addition, an anomalous hysteresis in fast strain and electric field sweeps is reported which may represent the predicted dynamical response of relaxing independent TLS.