  Dynamics of integrable systems, such as Tomonaga-Luttinger (TL) liquids, is
deterministic, and the absence of stochastic thermalization processes provides
unique characteristics, such as long-lived non-thermal metastable states with
many conserved quantities. Here, we show such non-thermal states can emerge
even when the TL liquid is excited with extremely high-energy hot electrons in
chiral quantum-Hall edge channels. This demonstrates the robustness of the
integrable model against the excitation energy. Crossover from the
single-particle hot electrons to the many-body TL liquid is investigated by
using on-chip detectors with a quantum point contact and a quantum dot. The
charge dynamics can be understood with a single-particle picture only for hot
electrons. The resulting electron-hole plasma in the TL liquid shows a
non-thermal metastable state, in which warm and cold electrons coexist without
further thermalization. The multi-temperature constituents are attractive for
transporting information with conserved quantities along the channels.
