Fig. 3.

Temporal dependence of correlated displacement field reveals characteristic time scales of active materials. (A) Normalized one-dimensional shear response, $U_{\overrightarrow{S}}$, for an active nematic (blue) and active gel (red) measured at different delay time $\tau$ (see scale bar). (B) Normalized shear response as a function of delay time $\tau$ measured at different spatial scales with respect to the critical length scale $R^{\ast }$. Experimental data are indicated with symbols solid lines are fit of the data to a stretched exponential. (C) Dynamic structure function $D(q,\tau )$ at different wave number $q$ (see scale). $D(q=2\pi /R^{\ast },\tau )$ is plotted in black. ${\tau }^2$ and $\tau$ scaling are indicated. (D) Characteristic time scales ${\tau }_r$ as a function of wave number $q$ for DDM (black) and displacement ($U_{\overrightarrow{u}}$, green), shear ($U_{\overrightarrow{S}}$, red), or vortical ($U_{\nu }$, blue) response.