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

TL;DR

This paper investigates the resonance structure and longevity of Floquet states in a dynamic fractional Stark ladder under high AC electric fields, revealing large peaks associated with long-lived states at high laser intensities.

Contribution

It introduces a non-perturbative analytical approach to analyze Floquet states in a fractional Stark ladder driven by terahertz laser fields, highlighting the manifestation of long-lived anomalous states.

Findings

Large peaks in excess density of states indicate long-lived Floquet states.

Longevity of states is prominent at high laser intensities.

Analytical expression captures ponderomotive couplings non-perturbatively.

Abstract

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.