Zener resonance in a dynamic Wannier-Stark ladder: Two miniband model

Quasienergy structures of Floquet states in strongly biased superlattices (with a static electric field of F-0) that are further driven by a sinusoidal electric field (with an amplitude of F-1) are calculated in a two miniband model when Zener resonance between the two minibands is significant. It is found that the quasienergies are affected pronouncedly by static and dynamic Zener tunnelings pertinent to F-0 and F-1, respectively, where both effects simultaneously couple Wannier-Stark ladder (WSL) subband states that are energetically aligned with each other. The dynamic Zener tunneling causes two lobes of quasienergy parent bands, which are ascribable to the different superlattice minibands and almost degenerate at F-1=0, to swerve sharply with increasing F-1. As F-1 becomes much larger, due exclusively to the static Zener tunneling, each split band undergoes a strong anticrossing with another lobe pertaining to the adjacent photon sideband. Furthermore, due mostly to the dynamic Zener tunneling, tendency toward band collapse or bandwidth narrowing characteristic of the usual dynamic WSL based on the single miniband picture is not observed here any longer for large F-0. On the contrary, bandwidth minima of one of the two split parent bands alternate with those of the other, and hence bandwidth narrowing does not occur simultaneously in every lobe at a single F-1.