Instability of dynamic localization in the intense terahertz-driven semiconductor Wannier-Stark ladder due to the dynamic Fano resonance

Abstract

The lifetime of an electronic Floquet state in a semiconductor Wannier-Stark ladder (WSL) driven by an intense monochromatic terahertz (THz) wave is examined based on the R-matrix Floquet theory, in which an excess density of states (DOS) corresponding to the lifetime is calculated. It is revealed that the dynamic localization (DL) characteristic of this system is unstable against Fano resonance (FR)-like interminiband decay mechanism caused by THz-mediated ac-Zener tunneling (ZT); in this study, this is termed as dynamic FR (DFR). The DFR is considered to be a new FR mechanism characterized by both tunable ac-ZT coupling and coexistence with shape resonance. The result obtained here is in sharp contrast with the conventional understanding without the introduction of DFR, in which the DL is very stable such that its lifetime is comparable to or greater than that of the associated WSL. It is found that the DFR mechanism generally becomes more dominant with an increase in the strength of the bias field. Further, we discuss the observation that the spectral pattern of the excess DOS is more involved for a single-photon resonant transition, namely, $\ensuremath{\Omega}=\ensuremath{\omega}$, than that for a two-photon resonant transition, namely, $\ensuremath{\Omega}=2\ensuremath{\omega}$, where $\ensuremath{\Omega}$ and $\ensuremath{\omega}$ represent a Bloch frequency and a THz frequency, respectively. In addition, the criterion for the applicability of the DFR to the present system is also obtained.