QUANTUM TRANSPORT-THEORY FOR ELECTRON-PHONON SYSTEMS IN STRONG ELECTRIC-FIELDS

We analyze transport in a uniform electric field of arbitrary strength by using a gauge-invariant formulation of the Airy representation of the Baym-Kadanoff-Keldysh theory of nonequilibrium quantum statistical mechanics. For a model electron-phonon interaction, experimentally relevant quantities can be extracted from a function of one variable; this function obeys a linear homogeneous integral equation. The quantum distribution function and the nonlinear drift velocity versus applied field characteristics are evaluated numerically. Many features of our nonlinear theory bear a formal resemblance to linear-response theory.