Evidence of growing spatial correlations during the aging of glassy   glycerol
  We have measured, as a function of the age $t_a$, the aging of the nonlinear dielectric susceptibility $\chi_3$ of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time $\tau_{\alpha}(t_a)$, this scaling breaks down for $\chi_3$, suggesting an increase of the amplitude of $\chi_3$. This is a strong indication that the number $N_{corr}$ of molecules involved in relaxation events increases with $t_a$. For $T=0.96 \times T_g$, we find that $N_{corr}$ increases by $\sim 10%$ when $t_a$ varies from $1\mathrm{ks}$ to $100\mathrm{ks}$. This sheds new light on the relation between length scales and time scales in glasses. 
C. Brun, F. Ladieu, L'H\^ote, G. Biroli, Jean-Philippe Bouchaud
cond-mat.soft cond-mat.mtrl-sci