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Plasmon-polariton gap soliton formation and transparency switching in one-dimensional nonlinear layered systems composed of alternate layers of a Kerr material and a dispersive linear metamaterial are theoretically studied. The behavior of the electric field profile inside the layered system is shown for different values of nonlinear power, linking the localized modes of the electric field with complete transparency states of the system. A detailed investigation on the influence of a defocusing nonlinearity on the transmission switching phenomenon, in the frequency range where the linear dispersion predicts the photon-plasmon coupling, is made, revealing different effects in the top and bottom edges of the plasmon-polariton gap. Specifically, we found a broadening of the plasmon-polariton gap when increasing the nonlinear power. In addition, a switching from very low to high transmission states is obtained and localized plasmon-polariton gap solitons of various orders are found for various values of frequencies and nonlinear strength.

We present a theoretical study of the nature of photonic band gaps of one-dimensional photonic crystals containing dispersive materials. Within the transfer-matrix formalism, we calculate the photonic band structure, transmission spectra and electric field profile for multilayered structures constituted by the periodic repetition of polaritonic and left-handed layers. It is suggested that the prediction of the existence of the 〈 n 〉 = 0 , plasmon-polariton, and ϕ e f f non-Bragg gaps, according to the frequency dependence of the permittivity and permeability of both layers, may be made simpler through the definition of more convenient quantities such as the generalized impedance and optical path length.

Purpose To assess the accuracy of three cone beam computed tomography (CBCT) systems in misfit detection at the implant-abutment joint. Materials and methods A total of 32 implants were placed in dry human mandibles. Porcelain-fused-to-metal crowns, both with and without a 200-μm-thick gap at the implant-abutment joint, were placed and then scanned using three CBCT systems: Picasso Trio (PT), OP300 (OP), and Scanora 3D (SC). Images were assessed, and area under the receiver operating characteristic curve (Az) values were compared (a = .05). Results Az values obtained with PT (0.86) were significantly higher than with OP (0.63) and SC (0.64) (P Conclusion Images acquired with PT allowed for more accurate misfit detection at the implant-abutment joint due to higher contrast resolution.

A theoretical study of one-dimensional heterostructures composed of alternate layers of a Kerr polaritonic material and a linear dispersive metamaterial is performed. For frequency values at the edges of the non-Bragg zero- ϕ eff gap of the heterostructure in the linear regime, a switching from very low to high transmission states is obtained and localized gap solitons of various orders are found, depending on the particular value of the incident power. Soliton solutions are shown to be robust with respect to absorption effects and a study is presented for gap soliton phases at the top and bottom of the zero- ϕ eff gap in the case of defocusing and focusing nonlinearities.

The localization properties of electromagnetic waves in one-dimensional disordered nonlinear-Kerr/metamaterial heterostructures are investigated. Structural disorder is introduced via a random fluctuation of layer widths of both nonlinear-Kerr and metamaterial slabs composing the photonic heterostructure. For frequency values in the vicinity of the zero− n gap, multiple electromagnetic modes with different transmission lengths are obtained for a given value of the Kerr defocusing nonlinearity power. Maximum-delocalized photonic states, which are associated with high-transmission electromagnetic modes corresponding to gap-soliton waves, are found to be quite sensitive with respect to the degree of disorder. Moreover, we have found that inclusion of absorption effects leads, as expected, to a decreasing of the transmission length.

The transmission properties of electromagnetic waves through a one-dimensional layered system containing alternate layers of air and a uniaxial anisotropic left-handed material are investigated. The optical axis of such heterostructure is along the stacking direction and the components of the electric permittivity and magnetic permeability tensors that characterize the metamaterial are modeled by a Drude-type response and a split-ring resonator metamaterial response, respectively. Different plasmon frequencies are considered for directions parallel and perpendicular to the optical axis. For oblique incidence, longitudinal bulk-like plasmon polariton modes are found in the neighborhood of the plasmon frequency along the optical axis and anisotropy leads to the unfolding of nearly dispersionless plasmon–polariton bands either above or below the plasmon frequency. Moreover, it is shown that, even in the presence of loss/absorption, these plasmon polariton modes do survive and, therefore, should be experimentally detected.

A systematic theoretical study of the transmission and reflection spectra of a 1D metamaterial heterostructure consisting of the finite repetition of a double layer of two different building blocks A (normal non-dispersive layer) and B (dispersive metamaterial) is presented, with the multi-layered system sandwiched between two semi-infinite layers of the A material. For the metamaterial slabs B we have studied two different dielectric/magnetic responses: a first one with both the electric permittivity and magnetic permeability given by a Drude-like metamaterial dispersion response, and a second one with the electric permittivity still given by a Drude-like response, whereas the magnetic permeability is given by a more realistic split-ring resonator metamaterial response. Theoretical calculations are performed within the transfer-matrix formalism, and transmission and reflection coefficients of the metamaterial heterostructure are straightforwardly evaluated. For oblique incidence, a finite projection along the growth direction of the electric or magnetic field of the incident wave associated with the TM or TE modes, respectively, leads to a coupling in each layer of the metamaterial heterostructure of the photon modes with the bulk electric or magnetic metamaterial plasmons, respectively. Such photon–plasmon coupling results in the formation of plasmon-polariton modes and gives rise to signatures of the electric or magnetic longitudinal bulk-plasmon polariton modes in the transmission and reflection spectra of the metamaterial heterostructure. Such features survive even in the case of a single AB double-layer metamaterial heterostructure, and experimental observation should be, therefore, easily achieved.

We perform a theoretical study of the bulk-plasmon polaritons in one-dimensional photonic superlattices made up of alternate layers of different metamaterials with dispersive dielectric permittivities and magnetic permeabilities for both normal and oblique incidence. We demonstrate that for oblique incidence a finite projection along the growth direction of the electric or magnetic field of the incident wave associated with the transverse-magnetic or transverse-electric modes, respectively, leads to a coupling in each layer of the heterostructure of the photon modes with the bulk electric or magnetic metamaterial plasmons, respectively. Such photon-plasmon coupling gives rise to electric or magnetic longitudinal bulk-plasmon polariton bands in the photonic band structure of the metamaterial–metamaterial superlattice. We also analyze the conditions for suppression of the longitudinal bulk-plasmon polaritons in the photonic band structure and reflection spectra of such metamaterial–metamaterial heterostructures.

The transmission and reflection properties of a meta-stack composed of a periodic AB arrangement of an air(A)/metamaterial(B) bilayer is presented, with the multi layered system embedded between two semi-infinite layers of the A material. For oblique incidence, a finite projection along the growth direction of the electric or magnetic field of the incident wave associated with the TM or TE modes, respectively, leads to a coupling of the photon modes with the bulk electric or magnetic metamaterial plasmons, in each layer of the meta-stack. This field-matter coupling gives rise to plasmon-polariton modes and signatures of electric or magnetic longitudinal bulk-plasmon polariton modes in the transmission, as well as in the reflection properties of the meta-stack, by means of a plasmon-polariton gap. Such features survive even in the case of a single bilayer and experimental observation should be, therefore, easily achieved.

Chylothorax is a well-recognized complication after neonatal cardiothoracic surgery. Management strategies include cessation of enteral feedings, repeated aspiration, chest drainage, and total parenteral nutrition. Somatostatin and its analogue, octreotide, have been used with promising results. The authors present three cases of neonatal postoperative chylothorax in which octreotide was used. After literature review, we can say that octreotide is relatively safe, and may reduce clinical course and complications associated with neonatal postoperative chylothorax. One should be aware of possible association between octreotide and necrotizing enterocolitis. Prospective controlled trials supporting octreotide use are lacking.

The effects of hydrostatic pressure on the conduction-electron effective Lande g-factor in semiconductor GaAs-Ga 1-x Al y As quantum wells under growth-direction and in-plane magnetic fields are studied. Calculations are performed by using the Ogg-McCombe effective Hamiltonian in order to take into account the non-parabolicity and anisotropy of the conduction hand. Numerical results are obtained as functions of the applied hydrostatic pressure and magnetic fields. Present results are in quite good agreement with experimental measurements in GaAs-Ga 1-x Al x As quantum wells in the absence of hydrostatic pressure, and indicate new possibilities for manipulating the electron-effective g-factor in semiconductor low-dimensional systems.

The effective electron Lande factor in GaAs – Ga 1 - x Al x As rectangular quantum well wires, under magnetic fields applied along the wire axis, is studied by taking into account the non-parabolicity and anisotropy of the conduction band within the Ogg–McCombe effective Hamiltonian. Confinement effects on the electron wavefunctions are explored in order to evaluate its influence on the behavior of the effective Lande factor. Calculations for the electron g ∥ factor in GaAs – Ga 1 - x Al x As rectangular quantum well wires are compared with the previous theoretical results obtained for GaAs – Ga 1 - x Al x As cylindrical quantum well wires. Such comparison clearly indicates the influence of the wire shape on the electron Lande factor in GaAs – Ga 1 - x Al x As quantum well wires.

We have used a variational procedure within the envelope-function and parabolic-band approximations to investigate the effects of hydrostatic pressure and crossed electric and magnetic fields on shallow-donor states in GaAs/Ga1-xAlxAs quantum wells. The donor variational envelope wave function is obtained through a hydrogenic 1s-like wave function and an expansion in a complete set of trigonometrical functions, and a detailed study is performed of the dependence of the donor binding energies on the applied hydrostatic pressure and applied in-growth direction electric and in-plane magnetic fields.

Using a variational procedure in the effective-mass and parabolic-band approximations we investigate the effects of in-plane magnetic fields on the exciton states in single GaAs/Ga1-xAlxAs quantum wells. Exciton properties are analyzed by using a simple hydrogen-like variational envelope wave-function. Present theoretical results are compared with available experimental measurements on the diamagnetic shift of the photoluminescence peak position of GaAs/Ga0.7Al0.3As quantum wells under in-plane magnetic fields [Phys. Rev. B 71 (2005) 045303].

A theoretical study of the direct and indirect exciton states in GaAs/Ga1-xAlxAs coupled double quantum wells under crossed electric and magnetic fields is presented. The setup of the system under consideration consists of an electric field perpendicular to the layers and an in-plane applied magnetic field. For calculations we use a variational procedure (by using a simple hydrogen-like envelope wave-function), in the effective-mass and parabolic-band approximations. Present theoretical results are found in fair agreement with available experimental measurements in double quantum well heterostructures under applied electric and magnetic fields.

Using the non-parabolic and anisotropic Ogg-McCombe effective Hamiltonian, we study the effect of the Dresselhaus spin splitting on the cyclotron effective mass and Landeg-factor associated to conduction electrons in GaAs-(Ga,Al)As quantum wells under applied magnetic fields, both along the growth- and in-plane directions of the heterostructure. Theoretical results are found in good agreement with available experimental measurements.

The band structure of a one-dimensional periodic array composed of two different layers of dimensions a and b characterized by refractive indices n 1 and n 2, respectively, is investigated. Refractive indices may take on positive as well as negative values. Within the Maxwell framework and using a transfer matrix technique for one dimensional periodic eigen-problems, we have determined a general equation, which governs the photonic band structure and the density of states (DOS) of one-dimensional photonic crystals. In addition to the well-known existence of the band gaps, we show that, depending on the width relationship b/a between the layer materials, super-lattices with null photonic band gap may exist and the conditions for such occurrences are established. Furthermore, we have been able to study the so-called 〈n〉 = 0 non-Bragg gap, ground ω0, for which the average refraction felt by the propagating radiation is null.

We perform a theoretical study, using a variational approach, of the effects of hydrostatic pressure on the exciton binding energies and photoluminescence peak positions in GaAs – Ga 1 - x Al x As cylindrical quantum-well wires within the effective-mass approximation. Calculated results suggest that future device applications may be realized by properly varying the wire dimensions and applying hydrostatic pressure.

We have investigated magnetic-field effects on the direct- and indirect-exciton dispersions and on the exciton effective mass in the plane perpendicular to the applied field, within the variational framework and effective-mass approximation, for coupled GaAs-(Ga,Al)As quantum wells. The simple hydrogen-like envelope wave function we have used provides the expected behavior for the exciton dispersion law in a wide range of the center-of-mass momenta, and leads to an analytical expression for the exciton effective mass. Theoretical results for the magnetic-field dependent exciton dispersion and effective mass are in quite good agreement with available experimental measurements.

The confinement effects on the electronic and donor states in GaAs–(Ga, Al)As quantum dots, in the presence of an applied magnetic field, are studied. Using the optical Bloch equations with damping, we study the time evolution of the 1s, 2p−, and 2p+ states in the presence of an applied magnetic field and of a terahertz laser. We discuss the conditions to obtain a bound 2p+ state in contrast to the bulk situation, where the 2p+ state is resonant with the continuum states (in this case, decoherence may be a serious problem for practical realizations). We show that the pronounced confining effects of semiconductor quantum dots lead to conditions such that the 2p+ excited donor state may lie below the continuum, originating a favourable situation concerning the coherence time of the corresponding Rabi oscillations. We also calculate the electric dipole transition moment, discuss the photosignal, and the possible experimental conditions under which decoherence is weak and qubit operations are efficiently controlled.

We present a theoretical investigation, in the effective-mass approximation, of exciton mixing and Is - 2p ± internal transitions of neutral magnetoexcitons in GaAs-Ga 1-x Al x As quantum wells. Theoretical results are obtained by diagonalizing the Kohn-Luttinger Hamiltonian in the presence of an external magnetic field along the growth direction of the quantum well, with mixing of appropriate light- and heavy-hole exciton states taken into account. We first perform the exciton calculations in the diagonal approximation, and take the exciton-envelope wave functions as linear combinations of products of hole and electron quantum-well states with Gaussian functions. Effects of exciton mixing are then calculated within perturbation theory. Theoretical results for the exciton internal transitions from 1s-like to 2p ± -like magnetoexciton states in GaAs-Ga 1-x Al x As quantum wells, with well widths of 80 A, 100 A, 125 A, 150 A and 200 A, are found in overall agreement with optically detected resonance measurements.

We have used the variational and fractional-dimensional space approaches, in the effective-mass approximation, in order to investigate the effects of applied magnetic fields on Coulomb-bound states, i.e. donor and exciton states, confined in GaAs–(Ga, Al)As quantum wells. In the variational procedure, we have used a simple hydrogenic-like envelope wavefunction whereas the anisotropic Coulomb-bound state+quantum well+magnetic-field system is modelled through an effective isotropic medium in the fractional-dimensional scheme. The magnetic fields are applied along the heterostructure growth direction, and calculations were performed for the binding energies, virial-theorem values and scaling properties. A virial-theorem value equal to 2 and a hyperbolic scaling for binding energies of Coulomb-bound states versus quantum-confined Bohr radii are obtained if one assumes a ground-state envelope wavefunction as a D-dimensional hydrogenic wavefunction, in contrast with results using the variational approach. Moreover, theoretical results within the variational approach lead to exciton-energy diamagnetic shifts in good agreement with available experimental measurements.

The effects of applied electric fields on donor and exciton states confined in GaAs–(Ga,Al)As quantum wells are studied in the effective mass approximation and within the variational and fractional-dimensional space approaches. In the fractional-dimensional scheme, an effective isotropic medium is used to model the anisotropic Coulomb-bound state + quantum well + electric-field system, whereas a hydrogenic-like wave function is used in the variational procedure. Results are obtained for the binding energies, virial-theorem values, and scaling properties of the Coulomb-bound states under growth-direction applied electric fields. We show that a ground-state wave function assumed as a D-dimensional hydrogenic wave function leads to a virial-theorem value of 2 and a hyperbolic scaling for binding energies of Coulomb-bound states versus quantum-confined Bohr radii, in contrast with results using the variational approach. Both methods result in Stark shifts for the exciton-peak energies in good agreement with electroabsorption experiments.

In the present work, we perform a comparison of theoretical approaches involving Coulomb-interaction corrections within the Hartree–Fock approximation and the renormalized dressed-band scheme in the large detuning limit. We focus on the well-studied optical Stark shift of the exciton peak in bulk and GaAs–(Ga,Al)As semiconductor quantum wells. It is argued that the Hartree–Fock scheme has severe limitations concerning its application to real experimental situations, even in the simplest laser field–perturbative regime. It is also shown, through a comparison between experiments and a three-band Kane-dressed GaAs–(Ga,Al)As quantum well calculation, that a proper treatment of band structure and confinement effects due to the quantum well is of fundamental importance in a theoretical understanding of Stark shift experimental measurements, and that the renormalized dressed-band approach is a very convenient tool to treat, in the large detuning limit, processes involving the laser–semiconductor interaction in l...

We have used the variational procedure and the fractional-dimensional space approach to study the effects of applied magnetic fields (perpendicular to the interfaces) in the virial theorem value and scaling of the shallow-donor binding energies versus quantum-sized donor Bohr radius in GaAs–(Ga,Al)As semiconductor quantum wells. In the fractional-dimensional space approach, one may show, under certain approximations, that the virial theorem value equals two and the scaling rule for the donor binding energy versus Bohr radius is hyperbolic for GaAs–(Ga,Al)As wells. In contrast, calculations within the variational scheme show that the scaling of the donor binding energies with a quantum-sized Bohr radius is, in general, non-hyperbolic and that the virial theorem value is non-constant. We conclude with a comparison with previous theoretical studies with respect to exciton states.

A detailed study of non-Bragg-gap solitons in one-dimensional Kerr-metamaterial quasiperiodic Fibonacci heterostructures is performed. The transmission coefficient is numerically obtained by combining the transfermatrix formalism in the metamaterial layers with a numerical solution of the nonlinear differential equation in the Kerr slabs, and by considering the loss effects in the metamaterial slabs. A switching from states of no transparency in the linear regime to high-transparency states in the nonlinear regime is observed for both zero-order and plasmon-polariton gaps. The spatial localization of the non-Bragg-gap solitons is also examined, and the symmetry properties of the soliton waves are briefly discussed.

Light shifts induced in the electronic and shallow on-center donor states in spherical semiconductor quantum dots, including magnetic field effects, are theoretically investigated. The interaction of light with the spherical GaAs–(Ga, Al)As quantum dot is treated within a dressed-band approach in which the Kane band structure scheme is used to model the GaAs bulk semiconductor whereas the dressing by the laser field is treated through the renormalization of the GaAs energy gap and conduction/valence effective masses. This nonperturbative approach is valid far from resonances and has been successfully adopted for other confined semiconductor heterostructures. The discrete nature of the electronic and impurity states, characteristic of quantum dot systems, and the possibility of adding extra confining effects by laser and applied magnetic fields opens up a promising route of applicability and/or manipulation of quantum-dot states in recent quantum-computer proposals.

The metric signature topological transitions associated with the propagation of electromagnetic waves in a dispersive metamaterial with frequency-dependent and anisotropic dielectric and magnetic responses are examined in the present work. The components of the reciprocal-space metric tensor depend upon both the electric permittivity and magnetic permeability of the metamaterial, which are taken as Drude-like dispersive models. A thorough study of the frequency dependence of the metric tensor is presented which leads to the possibility of topological transitions of the isofrequency surface determining the wave dynamics inside the medium, to a diverging photonic density of states at some range of frequencies, and to the existence of large wave vectors’ modes propagating through the metamaterial.

The variational and fractional-dimensional space approaches are used in a thorough study of the virial theorem value and scaling of the shallow-donor binding energies versus donor Bohr radius in GaAs/(Ga,Al)As semiconductor quantum wells (QWs) and quantum-well wires (QWWs). In the case of the fractional-dimensional space approach, in which the three-dimensional actual anisotropic semiconductor heterostructure is modelled by a fractional-dimensional isotropic effective medium, we have shown that if the ground-state wave function may be approximated by a D-dimensional hydrogenic wave function, the virial theorem value equals 2 and the scaling rule for the donor binding energy versus Bohr radius is hyperbolic, both for GaAs/(Ga,Al)As wells and wires. In contrast, calculations within the variational scheme show that the scaling of the donor binding energies with quantum-sized Bohr radius is in general nonhyperbolic and that the virial theorem value is nonconstant. Moreover, calculations for the donor binding energies versus well widths or wire radii, within both the fractional-dimensional and the variational approaches, indicate that any general conclusion based on a given virial theorem value or donor energy versus Bohr radius scaling rule should be examined with caution.

Shallow impurities and excitons in MBE-grown quantum-sized semiconductor low-dimensional systems are studied within the fractional-dimensional space approach. We present calculations for shallow-donor states in GaAs–(Ga,Al)As quantum wells and superlattices and for excitons in GaAs–(Ga,Al)As quantum wells and symmetric-coupled double quantum wells. Effects of growth-direction applied magnetic fields are also considered. Results are shown to be in good agreement with previous variational calculations and available experimental measurements.

A study of the effects of a laser field on the energy spectra of low-dimensional GaAs–(Ga,Al)As semiconductor systems is presented by using a Kane band-structure model for the GaAs bulk semiconductor. For a laser tuned far below any resonances, the effects of the laser–semiconductor interaction correspond to a renormalization or dressing of the semiconductor energy gap and conduction/valence effective masses. This renormalized approach may be used to give an adequate indication of the laser effects on any semiconductor heterostructures for which the effective-mass approximation provides a good physical description. As an application, it is shown that dressing effects on the donor and exciton peak energies in quantum-well heterostructures may be quite considerable and readily observable.

We have used the fractional-dimensional space approach to study the effects of applied magnetic fields on shallow-impurity states in GaAs–(Ga,Al)As quantum wells and superlattices. In this scheme, a semiconductor heterostructure is treated as isotropic in an effective fractional-dimensional space, and the value of the fractional dimension is associated to the degree of anisotropy introduced both by the heterostructure barrier potential and applied magnetic field. Theoretical fractional-dimensional calculations for shallow-impurity states in GaAs–(Ga,Al)As semiconductor quantum wells and superlattices, under magnetic fields applied along the growth direction, were shown to be in overall agreement with available experimental measurements and previous variational calculations.

The fractional-dimensional space approach is applied in the study of excitons and shallow impurities in semiconductor low-dimensional systems. In this scheme, a real anisotropic semiconductor heterostructure in a three-dimensional environment is treated as isotropic in an effective fractional-dimensional space, and the value of the fractional dimension is associated to the degree of anisotropy of the actual three-dimensional semiconductor system. When a magnetic field is applied along the growth direction of the semiconductor heterostructure, it introduces an additional degree of confinement and anisotropy besides the one imposed by the heterostructure barrier potential. The fractional dimension is then related to the anisotropy introduced both by the heterostructure barrier potential and magnetic field. In this work, we present results for excitons in GaAs–(Ga,Al)As quantum wells and symmetric-coupled double quantum wells, and shallow-impurity states in GaAs–(Ga,Al)As quantum wells and superlattices under growth-direction applied magnetic fields. Results are shown to be in good agreement with available experimental measurements and previous variational calculations.

A variational procedure in the effective-mass approximation was used in the study of both the density of donor states and the associated optical absorption spectra of GaAs-(Ga,Al)As semiconductor heterostructures. Calculations were performed for a finite, cylindrical-shaped quantum box of GaAs within the infinite-barrier approximation and considering an homogeneous distribution of impurities within the low-dimensional heterostructure. Theoretical results for the density of impurity states and donor-related optical absorption spectra were found to be in good agreement with previous studies in the limiting cases of quantum wells and quantum-well wires.

A theoretical study of the exciton diamagnetic shifts in GaAs-Ga1-xAlxAs quantum dots (QDs) and ultrathin quantum wells (QWs), under growth-direction applied magnetic-fields, is performed. We work in the effective-mass approximation and take into account nonparabolicity effects for the effective masses of both the conduction and valence bands. Calculated results for the diamagnetic shifts of the m=0 ground-state, m=-1 and -2 excited states of the heavy-hole exciton, within a simple "QD+ultrathin QW" model heterostructure, are found in overall agreement with recent experimental measurements by Schildermans et al. (Phys. Rev. B 72 (2005) 115312) and Sidor et al. [Phys. Rev. B 73 (2006) 155334].

We use the Ogg–McCombe Hamiltonian together with the Dresselhaus and Rashba spin-splitting terms to find the g factor of conduction electrons in GaAs-(Ga,Al)As semiconductor quantum wells (QWS) (either symmetric or asymmetric) under a magnetic field applied along the growth direction. The combined effects of non-parabolicity, anisotropy and spin-splitting terms are taken into account. Theoretical results are given as functions of the QW width and compared with available experimental data and previous theoretical works.

A systematic study of the longitudinal effective mass associated with either shallow impurity states or conduction Landau levels under in-plane magnetic fields is presented for Fibonacci superlattices. We analyze the relation between the mean longitudinal effective masses and the localization length of the corresponding electronic or impurity states. Under appropriate conditions we show that the mean longitudinal effective mass weakly depends on the nature of the electron state and localization length, and is essentially related to the Cantor-like energy spectra or ``band structure.''

A theoretical resonant-tunnelling approach is used in a detailed study of the electronic and transmission properties of quasiperiodic Fibonacci GaAs-(Ga,Al)As semiconductor superlattices, under applied electric fields. The theoretical scheme is based upon an exact solution of the corresponding Schroedinger equations in different wells and barriers, through the use of Airy functions, and a transfer-matrix technique. The calculated quasibound resonant energies agree quite well with previous theoretical parameter-based results within a tight-binding scheme, in the particular case of isolated Fibonacci building blocks. Theoretical resonant-tunnelling results for and generations of the quasiperiodic Fibonacci superlattice reveal the occurrence of anticrossings of the resonant levels with applied electric fields, together with the conduction- and valence-level wave function localization properties and electric-field-induced migration to specific regions of the semiconductor quasiperiodic heterostructure. Finally, theoretical resonant-tunnelling calculations for the interband transition energies are shown to be in quite good quantitative agreement with previously reported experimental photocurrent measurements.

We have used the transfer-matrix approach for one-dimensional Cantor photonic superlattices, and studied the plasmon-polariton modes for a multilayered system composed by alternating layers of positive and dispersive materials. Results indicate that the corresponding plasmon-polariton modes, which show up for oblique incidence, strongly depend on the Cantor step, and the plasmon-polariton subbands are associated with the number of metamaterial layers contained in the elementary cell. Moreover, we have studied the 〈n〉 = 0 non-Bragg gap in such fractal photonic superlattices and characterized its behavior as function of the steps of the Cantor series.

The effects of traps and shallow acceptors on the continuous-wave steady-state photoluminescence of GaAs-(Ga,Al)As quantum-well wires are studied at room temperature. The analysis is based on a quantum-mechanical calculation of the transition rates of radiative recombinations of excited-conduction electrons with free and bound (at acceptors) holes, and on a phenomenological treatment of the nonradiative rates associated with transitions involving conduction electrons falling into traps, and trapped electrons recombining with free holes. The various steady-state radiative and nonradiative e-h recombination lifetimes as function of the cw laser intensity are then obtained, as well as the dependence of the conduction-electron quasi-Fermi level (or chemical potential), and carrier densities on the laser intensity. We have also studied the laser-intensity dependence of various recombination efficiencies and of the integrated photoluminescence intensity. Finally, trap and impurity effects are shown to be quite important in a quantitative understanding of the room temperature steady-state photoluminescence of quantum-well wires.

The acceptor-related photoluminescence of a GaAs–(Ga,Al)As superlattice, under the influence of a magnetic field applied parallel to the interfaces, is theoretically studied following a variational procedure within the effective-mass approximation. Electron and hole magnetic Landau levels and envelope wave functions were obtained by an expansion in terms of sine functions, whereas for the impurity levels the envelope functions were taken as products of sine and hydrogenic-like variational functions. Impurity binding energies and wave functions are obtained for acceptors at a general position in the superlattice and for different in-plane magnetic fields. Theoretical results corresponding to transitions from the conduction subband to states of acceptors (miniband-to-acceptor e−A0 transitions) at the edge and center positions of the GaAs quantum well compare well with available experimental data by Skromme et al. [Phys. Rev. Lett. 65, 2050 (1990)] on the magnetic-field dependence of the photoluminescence pe...

The effects of applied magnetic fields on the optical absorption spectra associated with transitions from the Landau valence magnetic levels to shallow donor states in GaAs - (Ga, Al)As quantum wells are studied for magnetic fields applied perpendicular to the heterostructure interfaces. The donor-related magneto-absorption spectra are calculated within the effective-mass approximation, and with a minimization procedure for evaluating donor energies and envelope wave functions. We consider a homogeneous donor distribution in the well and analyse the theoretical impurity-related magneto-absorption spectra for various quantum well widths and applied magnetic fields. The magneto-absorption lineshapes present features clearly associated with transitions involving donor states and different valence Landau magnetic levels.

An extensive theoretical study of the magneto-optical absorption spectra of periodic GaAs - (Ga, Al)As superlattices under magnetic fields parallel to the heterostructure interfaces is presented within the framework of the effective-mass approximation. The absorption coefficient associated with interband transitions between valence-hole and conduction-electron magnetic levels is calculated by considering an expansion of the envelope wavefunctions in terms of sine functions and by adopting a parabolic-band model for both electrons and holes. Results for the theoretical magneto-optical interband absorption spectra for varying in-plane magnetic fields compare qualitatively well with various experimental measurements. We present a detailed analysis of the effects of off-diagonal interband transitions involving conduction and valence Landau levels n and , respectively, with , and it is unambiguously shown that off-diagonal transitions may introduce significant contributions and extra features in the magneto-optical absorption spectra.