Optical investigation of electric-field-induced relaxations in amorphous solids at low temperatures

The influence of external electric fields on low-temperature relaxations in polymer glasses has been discovered and investigated in the temperature regime of 50-700 mK. An external field pulse, applied to polymer samples, creates nonequilibrium populations in the ensemble of specific local low-energy excitations (TLS). This manifests itself in a reversible nonequilibrium contribution to spectral diffusion (SD), which was monitored via the method of spectral hole burning. The temperature dependence of the electric-field-induced SD as well as the dependence on both field strength and pulse duration are investigated and quantitatively interpreted in the framework of an extended TLS model. The average value of the static electric dipole moment of TLS is measured for two polymers: PMMA and PS. The agreement of our experimental data with the model calculations is very good. (C) 1998 Elsevier Science B.V. All rights reserved.