Off equilibrium fluctuations in a polymer glass.

Abstract : The fluctuation-dissipation relation (FDR) is measured on the dielectric properties of a polymer glass (polycarbonate). It is observed that the fluctuation dissipation theorem is strongly violated after a quench from above to below the glass transition temperature. The amplitude and the persistence time of this violation are decreasing functions of frequency. Around $1Hz$ it may persist for several hours. The origin of this violation is a highly intermittent dynamics characterized by large fluctuations and strongly non-Gaussian statistics. The intermittent dynamics depends on the quenching rate and it disappears after slow quenches. The relevance of these results for recent models of aging are discussed.