Nonstationary quasiperiodic energy distribution of an electron gas upon ultrafast thermal excitation

We consider the evolution of an electronic system initially in equilibrium with a semiconductor crystal lattice upon a sudden rise in the lattice temperature. On a short time scale ({~}1 ps), electrons equilibrate with the optical phonons and establish a peculiar quasiperiodic energy distribution. Time evolution toward this distribution is discussed on the basis of an exact solution of the Boltzmann transport equation. While the quasiequilibrium regime persists (longer than {~}1 ns), the electronic system possesses a number of unusual thermodynamic and transport properties. The specific heat is suppressed as if some of the electronic degrees of freedom of were frozen out; the low-field electron mobility is substantially enhanced.