P. Aceituno

Coherent response of a biased double-well superlattice subjected to an ultrashort interband excitation

The temporal evolution of electrons in a biased double-well superlattice, subjected to an ultrashort interband excitation, is theoretically examined. Both the temporal oscillations of the induced current and the evolution of the photoexcited electron concentration are considered for different parameters of the structure subjected to a δ-pulse excitation. Due to the mixing of the Wannier–Stark-ladder branches, the induced response depends on the applied bias voltage in a complicated way. In particular, long-time beats appear in the vicinities of intra- and inter-cell anti-crossings of the energy spectrum. These dependencies are examined within the framework of the Kane model, invoking the parabolic approximation for electron and heavy hole states. Numerical calculations of the carrier coherent dynamics are performed for the case of a δ-pulse excitation and with a phenomenologically introduced damping factor.

Quantum tunnelling of electrons through a GaAs-Ga1-xAlxAs superlattice in a transverse magnetic field: an analytical calculation of the transmission coefficient

The transmission coefficient for tunnelling through double barriers and superlattices of GaAs-Ga1-xAlxAs, under transverse-magnetic-field action, has been calculated using a transfer matrix model. In this work, the one-dimensional effective-mass equation has been first solved analytically by means of the confluent hypergeometric functions as envelope functions

Ultrafast photoexcitation and coherent dynamics of electrons in triple tunnel‐coupled quantum wells

Coherent dynamics of electrons in the triple tunnel‐coupled quantum wells after an ultrafast optical excitation is studied. In a collisionless approximation, we consider temporal evolution of the electron distribution for different parameters of structure and pulse duration. Due to mixing of the tunneling frequencies under the three‐level tunneling resonance condition, transient evolution of the dipole moment demonstrates different kinds of behavior: harmonic oscillations, beats, and nonperiodic oscillations.

Electron energy spectrum and density of states for nonsymmetric semiconductor heterostructures in an in-plane magnetic field

Modifications of spin-splitting dispersion relations and density of states for electrons in nonsymmetric heterostructures under in-plane magnetic field are studied within the envelope function formalism. Spin-orbit interactions, caused by both a slow potential and the heterojunction potentials (which are described by the boundary conditions) are taken into account. The interplay between these contributions and the magnetic field contribution to the spin-splitting term in the Hamiltonian is essential when energy amount resulting from the Zeeman and spin-orbit coupling are of the same order. Such modifications of the energy spectra allow us to separate the spin-orbit splitting contributions due to a slow potential and due to the heterojunctions. Numerical estimates for selectively-doped heterojunction and quantum well with narrow-gap region of electron localization are performed. PACS numbers: 72.25.-b, 73.21.-b

Asymmetric doping effects on electronic properties of coupled quantum wells in an in-plane magnetic field

The purpose of this work is to study the influence of asymmetric doping positions on the electronic properties of tunnel-coupled double quantum wells (DQWs) in an in-plane magnetic field. The doping asymmetry introduces peculiarities in the gap due to the anticrossing of the two branches of the electronic dispersion relations. The built-in potential caused by the doping dramatically affects the self-consistent Fermi energy renormalization and strongly opposes an applied bias. As a result, the magnetization shows an abrupt jump when the transition from vertical to horizontal anticrossing occurs. The absolute value of the magnetoinduced voltage of two dimensional electrons in DQWs increases if the Fermi level is localized near such peculiarities and shows additional features in comparison with the symmetric-doping case. We suggest that the transverse voltage induced by a magnetic field and the magnetization are powerful tools for the experimental study of doping characteristics and equilibrium magnetic prop...

Electron‐phonon interaction and tunneling escape process in GaAs/AlAs quantum wells

In this work, we have numerically integrated in space and time the effective mass Schrodinger equation for an electron in a GaAs/AlAs quantum well. Considering the electron–phonon interaction and an external electric field, we have studied the electronic tunneling escape process from semiconductor quantum wells. In this way, electronic lifetimes have been obtained at different well widths and applied electric fields.

Dynamical Jahn-Teller effect in Pb2+ doped alkali halides

Abstract A systematic investigation of the line shape of the A band in Pb2+ doped NaCl, KCl and RbCl has been carried out in the temperature range of 10–300 K. A doublet structure in the A absorption band has been observed. The temperature dependence of the splitting between the two components as well as their relative change in intensity is explained considering a dynamical Jahn-Teller effect.

Valence band dispersion in finite quantum wells with uniform electric field

Abstract Valence band dispersion of GaAs-Ga1-xAlxAs single finite quantum well in presence of an external electric field is computed by means of the perturbed Luttinger Hamiltonian, when the field is perpendicular to the semiconductor layers. We use an iterative process to solve the set of coupled differential equations, taking into account only the mixing of the deepest bounded valence states. This situation is important for the second and third valence band levels in the k-space.

Intersubband optical absorption in InSb stepped quantum wells: Effect of spin sublevels crossing

Abstract We study linear and non-linear coefficients of the intersubband absorption in InSb-based stepped quantum wells subjected to an in-plane magnetic field. We consider also a transverse electric field to achieve near resonance conditions. Taking into account the two deepest conduction levels and their corresponding Zeeman spin splitting sublevels, we calculate dispersion relations by means of an improved version of Kane model. Besides the known anti-crossing between down and up spin split sublevels, we obtain an extra spin level crossing for some determined parameters. This crossing clearly modifies the absorption spectrum for transitions among the four sublevels considered. We study a low electron density case, when only the first deepest sublevel is occupied, and a high density case with only the highest sublevel empty. We find a similar behavior of the absorption spectrum in both cases.

Temporal stimulated intersubband emission of photoexcited electrons

We have studied the transient evolution of electrons distributed over two levels in a wide quantum well, with the two levels below the optical phonon energy, after an ultrafast interband excitation and cascade emission of optical phonons. If electrons are distributed near the top of the passive region, a temporal negative absorption appears to be dominant in the intersubband response. This is due to the effective broadening of the upper level state under the optical phonon emission. We have then considered the amplification of the ground mode in a THz waveguide with a multiquantum well placed at the center of the cavity. A huge increase of the probe signal is obtained, which permits the temporal stimulated emission regime of the photoexcited electrons in the THz spectral region.