Manifestation of anomalous Floquet states with longevity in dynamic fractional Stark ladder with high AC electric fields

We examine a resonance structure of Floquet state in dynamic fractional Stark ladder (DFSL) realized in biased semiconductor superlattices driven by a terahertz cw laser on the basis of the R-matrix Floquet theory. To do this, we calculate an excess density of state rho((ex))(E) corresponding to lifetime of the Floquet state with a fractional matching ratio eta, where eta is the ratio of a Bloch frequency Omega(B) to a laser frequency omega, namely, eta = Omega(B)/omega. The results for eta = 3/2 demonstrate the appearance of discernibly large peaks associated with Floquet states with longevity in a region of relatively high laser-intensity. The underlying physics is discussed in terms of an analytical expression of rho((ex)) (E) and the associated Green function in which ponderomotive couplings are included in a non-perturbative way. (C) 2016 Elsevier B.V. All rights reserved.