Heterogeneity and cooperativity in glassy dynamics investigated by nonlinear dielectric spectroscopy
Glassy materials such as polymers, glass fibers, metallic glasses and, of course, the large variety of applications of silicate glasses govern our daily live. However, the glass transition is still considered one of the most challenging mysteries in condensed-matter physics. Refining the technique of nonlinear dielectric spectroscopy, we gain new information about two characteristic features of glassy dynamics:
First, we present high-field permittivity spectra of two glass-forming liquids that show nonlinear behavior which can be explained within the framework of heterogeneously distributed molecular relaxation times. Interestingly, this nonlinear effect happens to be absent in the so-called excess-wing regime, that could not be accessed by this method before.
Second, we report detailed measurements of the third-order nonlinear dielectric susceptibility of four glass-forming systems for a broad temperature range. Our experiments finally prove the old notion that intermolecular correlations of glassy systems are responsible for the non-canonical temperature development of glassy dynamics.