Aging and effective temperatures near a critical point.

The orientation fluctuations of the director of a liquid crystal are measured after a quench near the Fréedericksz transition, which is a second order transition driven by an electric field. We report experimental evidence that, because of the critical slowing down, the liquid crystal presents several properties of an aging system after the quench, such as power law scaling in times of correlation and response functions. During this slow relaxation, a well defined effective temperature, much larger than the heat bath temperature, can be measured using the fluctuation dissipation relation.