Random Lattices in Combined a.c. and d.c. Electric Fields: Anderson vs. Wannier-Stark Localization

Employing a single-band tight-binding model with random diagonal disorder, we study localization of quasi-energy states in the presence of both static and resonant oscillating electric fields. A characteristic minimum strength of the a.c. field is required for effective destruction of the localization induced by the d.c. field. The numerically determined dependence of this characteristic a.c. field amplitude on the disorder strength confirms that the localization of wave packets in disordered lattices under simultaneous d.c. and resonant a.c. bias is entirely analogous to the familiar Anderson mechanism in the absence of external fields, but with field-renormalized quasi-energy bands playing the role of energy bands in the field-free case.