Evidence of growing spatial correlations at the glass transition from nonlinear susceptibility measurements

Abstract

International audienceThe ac nonlinear dielectric response 3ð!; TÞ of glycerol was measured close to its glass transitiontemperature Tg to investigate the prediction that supercooled liquids respond in an increasingly nonlinearway as the dynamics slows down (as spin glasses do). We find that 3ð!; TÞ indeed displays severalnontrivial features. It is peaked as a function of the frequency ! and obeys scaling as a function of !ðTÞ,with ðTÞ the relaxation time of the liquid. The height of the peak, proportional to the number ofdynamically correlated molecules NcorrðTÞ, increases as the system becomes glassy, and 3 decays as apower law of ! over several decades beyond the peak. These findings confirm the collective nature of theglassy dynamics and provide the first direct estimate of the T dependence of Ncor