Universal Fermi distribution of semiclassical nonequilibrium Fermi states

When a classical device suddenly perturbs a degenerate Fermi gas, a semiclassical nonequilibrium Fermi state arises. Similar states appear when a charge is transferred into a Fermi gas through a localized contact. Semiclassical Fermi states are characterized by a Fermi energy or Fermi momentum that slowly depends on space and/or time. We show that the Fermi distribution of a semiclassical Fermi state has a universal nature. It is described by Airy functions regardless of the details of the perturbation.