Onset of topological quantum chaos in strongly correlated electron systems.

We address manifestations of quantum chaos at temperatures $T$ far below the Debye temperature $T_D$ associated with the onset of classical behavior, effects that are well documented in experimental studies of strongly correlated electron systems. We attribute this unexpected phenomenon to spontaneous rearrangement of the conventional Landau state beyond a critical point at which the {\it topological} stability of this state breaks down, leading to the formation of an interaction-induced flat band adjacent to the nominal Fermi surface. We demonstrate that beyond the critical point, the quasiparticle picture of such correlated Fermi systems still holds, since the damping of single-particle excitations remains small compared with the Fermi energy $T_F=p^2_F/2m_e$. A Pitaevskii-style equation for determination of the new quasiparticle momentum distribution $n_*({\bf p})$ is derived, which provides for explanation of the linear-in-$T$ behavior of the resistivity $\rho(T)$ found experimentally. The interplay between this scenario for non-Fermi-liquid behavior of $\rho(T)$ and an alternative picture based on the notion of Planckian dissipation is discussed.