Dynamic Fano resonance of Floquet-state excitons in superlattices

Abstract

The dynamic Fano resonance (DFR) between discrete quasienergy excitons and sidebands of their ionization continua is predicted and investigated in dc-and ac-driven semiconductor superlattices. This DFR, well controlled by the ac field, delocalizes the excitons and opens an intrinsic decay channel in nonlinear four-wave mixing signals.PACS numbers: 71.35. Cc, 42.50.Md, 78.20.Jq, 78.47.+p The Fano resonance (FR) results from quantum coupling between a discrete state and a degenerate continuum of states and manifests itself in optical spectra as asymmetric lineshape [1]. FR was observed in a variety of atomic and molecular systems. Recently, this phenomenon has been reported in semiconductor quantum wells [2], in biased semiconductor superlattices (SSL's) [3], and in bulk GaAs in the presence of magnetic field [4,5] where discrete excitons couple to continua of the lower transitions through Coulomb interaction [6]. In addition to the frequency-domain experiments, transient four-wave mixing (FWM) in magneto-confined bulk semiconductors [5] and in SSL's [3] has demonstrated that the FR is a fundamental type of dephasing mechanism in irreversible quantum dynamical processes.An intense ac field, e.g. the free electron laser, can induce the dynamical localization (DL) [7] of electrons in SSL's. The DL is directly related to the collapse of the quasienergy band of Floquet states [8][9][10], the temporal analogue to the Bloch states in spatially periodic potential [11]. Research taking into account Coulomb interaction has shown that the DL may cause the dimension crossover of excitons [12] and the enhancement of exciton binding and opacity in linear [12,13] and nonlinear spectra [14]. Meanwhile the dynamical delocalization (DDL) effect of an ac field is also investigated on localized Wannier-Stark (WS) states [15] in biased SSL's [9,10,14], which is hindered by Coulomb binding [14].In this Letter, we predict the dynamic Fano resonance (DFR) between quasienergy exciton states in biased SSL's driven by an intense THz-field. In particular, the novelty of this DFR consists in the coupling between the discrete quasienergy exciton and the neighbor sideband of its ionization continuum. This DFR will also lead to the dynamical ionization of bound excitons in SSL's, which itself is a new effect of the ac field.The one-dimensional tight-binding model [14,16] is adopted in the present investigation. With excluding the realistic three-dimensional excitonic motion, the results are hardly compared to experimental data quantitatively, but we believe this simple model does present qualitatively correct results, in view of the fact that the ground WS exciton-state usually possesses much larger oscillator strength than its ionization continuum of inplane motion, and the coupling induced by the ac field between the in-plane motion associated with different WS states is negligible because of their approximate orthogonality. The Coulomb interaction is treated on the basis of Hartree-Fock approximation. The neglected genuine many-body corr...

Theory of excitonic high-order sideband generation in semiconductors under a strong terahertz field

“…The Hamiltonian is time periodic and can be treated in Floquet representation. 15 The quasienergies and quasienergy states read, respectively ͑see Appendix A͒…”

Instability of Dynamic Localization in the Intense THz-Driven Semiconductor Wannier-Stark Ladder due to the dynamic Fano resonance

“…For the study of a DWSL exciton, Ref. [40] used the terminology of DFR in a different sense in which the THz wave was so weak that ac-ZT was of no importance, and hence, the Fano resonance (FR) was caused simply by a Coulomb interaction. In addition, the nonlinear Fano effect was discussed in semiconductor QWs and quantum dots in Refs.…”

“…+ jω, is rewritten as ε bj = ϵ bN wsl + λω(40) within a single-miniband nearest-neighbor-tight-binding approximation, where ϵ(c) b is the center of the energy of the bth SL-miniband and ϵ bN wsl is a WSL energy level corresponding to the bth miniband with a WSL index N wsl = 0, ±1, ±2, • • • , namely, ϵ bN wsl = ϵ (c) b + N wsl Ω, and hence, λ = j − nN wsl is defined. This relation implies that the DL state with the quantum number (b, j) introduced in Sec.…”

Exciton absorption in semiconductor superlattices in a strong longitudinal THz field

“…When an SSL is irradiated with radiation from an intense THz laser and probed by a weak near-bandgap laser, a wealth of physical phenomena may be observed, including the dynamical Franz-Keldysh effect (DFKE) [1], the ac Stark effect (ACSE) [2,3], the dynamical localization (DL) and delocalization [4,5], the inverse Bloch oscillations [6]- [10], the dynamical Fano effect [11], the exciton stabilization [12] and the high-order THz-sideband generation [13,14].…”