  Analyses of thermal diffusivity data on complex insulators and on strongly
correlated electron systems hosted in similar complex crystal structures
suggest that quantum chaos is a good description for thermalization processes
in these systems, particularly in the high temperature regime where the many
phonon bands and their interactions dominate the thermal transport. Here we
observe that for these systems diffusive thermal transport is controlled by a
universal Planckian time scale $\tau\sim \hbar/k_BT$, and a unique velocity
$v_E$. Specifically, $v_E \approx v_{ph} $ for complex insulators, and $v_{ph}
\lesssim v_E \ll v_{F}$ in the presence of strongly correlated itinerant
electrons ($v_{ph}$ and $v_F$ are the phonons and electrons velocities
respectively). For the complex correlated electron systems we further show that
charge diffusivity, while also reaching the Planckian relaxation bound, is
largely dominated by the Fermi velocity of the electrons, hence suggesting that
it is only the thermal (energy) diffusivity that describes chaos diffusivity.
