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 THz wave is examined based on the R-matrix Floquet theory, in which an excess density of state (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 inter-miniband decay mechanism caused by THz-mediated ac-Zener tunneling; in this study, this is termed as dynamic Fano resonance (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, Ω = ω, than that for a two-photon resonant transition, namely, Ω = 2ω, where Ω and ω 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.

Quasienergy resonance in a dynamic Wannier-Stark ladder

“…2 and 3 of Ref. 19. A similar tendency also applies for [1/m] μν (z), though its effect is considered weaker than that of V μν (z) because of the small difference of the masses in the barrier and well regions of the SL potential.…”

“…[15][16][17] Strictly speaking, the DWSL problem should be dealt with as a problem with open boundary conditions, namely, the scattering problem. 18,19 The reason for this is obviously understood by making the Kramers-Henneberger transformation 20,21 of the original tilted-SL-potential flapping temporally with a laser frequency into a photodressed potential, as will be shown later in more detail. 22 This intersite ac-ZT effect is reminiscent of the dc-ZT effect in WSL, where the WSL levels attributed to different SL minibands are coupled to each other, leading to delocalization of electronic states across several WSL sites; in particular, such delocalization stands out when Zener resonance takes place.…”

“…In particular, the case of η = 1 is most important because the effect of PAT is maximized. This paper is aimed at revealing detailed physical mechanisms governing the DWSL, since our preceding study 19 did not delve deeply into this subject. Hereafter, the conventional quasienergy picture is referred to just as the quasienergy picture when compared with the results based on the excess DOS picture; the results obtained in Ref.…”

“…40,41 The present study is regarded as the further developed study of Ref. 19 toward a comprehensive understanding of the DWSL with η integer. In particular, the case of η = 1 is most important because the effect of PAT is maximized.…”

“…Thus, this method is considered to be closely related to the complex quasienergy method with a complex basis set. Meanwhile, the above-mentioned Rmatrix Floquet theory was already applied to the DWSL problem, 19 illustrating the instability of dynamic localization due to dynamic Fano resonance by employing the excess DOS. Further, this has been applied to the study of a more complicated excitonic Floquet problem of the DWSL.…”