Near-frozen non-equilibrium state at high energy in an integrable system

Ergodic many-body systems are expected to reach quasi-thermal equilibrium. Here we demonstrate that, surprisingly, high-energy electrons, which are injected into a quantum Hall edge mode with finite range interactions, stabilize at a far-from-thermalized state over a long time scale. To detect this non-equilibrium state, one positions an energy-resolved detector downstream of the point of injection. So far, non-equilibrium distributions in integrable systems were either found not to display relaxation at all, or generically relax to near-thermal asymptotic states. In stark contrast, the here-obtained many-body state comprises fast-decaying transient components, followed by a nearly frozen distribution with a peak near the injection energy.