Fano Resonances in Semiconductor Superlattices

Abstract

We report the first observation of Fano resonances in biased semiconductor superlattices: The excitonic Wannier-Stark ladder transitions show asymmetric absorption due to the coupling to the continua of lower transitions. In contrast to other known examples of Fano resonances, the Fano coupling can be continuously tuned in this system by changing the static field across the superlattice. The line shapes and their coupling dependence are in excellent agreement with theory. We also investigate the dephasing dynamics of the resonances and observe an increase in dephasing with increasing Fano coupling. [S0031-9007(98)06702-7]

Franz-Keldysh effect and dynamical Franz-Keldysh effect of cylindrical quantum wires

“…[1][2][3][4] Extensive work has been done to investigate the specifics of the excitonic optical properties of quantum wells, 1,2 quantum wires, [3][4][5][6] quantum dots, [7][8][9][10] and superlattices. [11][12][13][14][15][16] The optical spectra of semiconductor structures can be modified dramatically by the application of external static electric and/or magnetic fields. For semiconductor quantum wells, the Franz-Keldysh ͑FK͒ effect occurs when an electric field polarized in the plane of the quantum wells is applied, while the quantum-confined Stark effect prevails for a field polarized in the growth direction.…”

Dynamic Fano resonance of Floquet-state excitons in superlattices

“…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.…”

“…3 (c), follows approximately the Fano coupling parameter γ [ Fig. 3 (b)], indicating that the DFR plays a role in intrinsic phase-breaking process as the usual FR does in biased SSL's [3,19].…”

“…The neglected genuine many-body correlation [17] may lead to almost instantaneous decay in time-integrated (TI) FWM signals, which is irrelevant to the intrinsic dephasing [5]. This effect is crucial for the magneto-confined FR [5] due to the magnetic field-induced enhancement of many-body correlation [18], but is less important for the decay of TI-FWM signals in biased SSL's, which is, in essence, an intrinsic dephasing process [3,19].The semiconductor Bloch equations in the presence of electric fields [16] for the exciton amplitude p k ≡ a h−k a ek and electron-hole (e-h) pair densitywhere a ek (a hk ) is the electron (hole) annihilation operator for the quasi-momentum state |e(h), k , E 0 is the separation between centers of the conduction and the valence minibands, ε k (t) = ε k −2 k ′ V k,k ′ f k ′ is the renormalized combined e-h miniband dispersion with ε k = − ∆ 2 cos k, ω BO is the Bloch oscillation frequency due to the dcfield [20], ω 1 is the strength of the driving ac field with frequency ω, χ R (t) = χ(t) + k ′ V k,k ′ p k ′ is the renormalized strength of a near infrared optical excitation (here the dipole element is assumed k-independent), and V k,k ′ comes from the Coulomb potential.The Schrödinger equation for the exciton wave function is just the linear part of Eq. (1) with the excitation and dephasing terms removed.…”

“…The neglected genuine many-body correlation [17] may lead to almost instantaneous decay in time-integrated (TI) FWM signals, which is irrelevant to the intrinsic dephasing [5]. This effect is crucial for the magneto-confined FR [5] due to the magnetic field-induced enhancement of many-body correlation [18], but is less important for the decay of TI-FWM signals in biased SSL's, which is, in essence, an intrinsic dephasing process [3,19].…”