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A theoretical study of the photonic band structure and transmission spectra for 1D periodic superlattices with an elementary cell composed of two layers of refractive indices n(a) and n(b), which may take on positive as well as negative values, has been performed within the transfer-matrix approach. The dependence on the angle of incidence of the electromagnetic wave for excitation of plasmon-polaritons as well as the properties of the (n) = 0 gap were thoroughly investigated. Results are found for the generalized conditions that must be satisfied by the ratio a/b of the layer widths of metamaterial photonic superlattices, for both transverse electric and transverse magnetic polarizations, in order to have an omnidirectional (n) = 0 gap. The present study indicates new perspectives in the design and development of future optical devices.

The complex emitter dynamics expected to appear in structured reservoirs, such as bandgap photonic crystals, is shown to be observed via an implementation based on spin chains. We have demonstrated that such association yields new ways of engineering spin chains for efficient state transfers.

The effects of a laser field on the conduction-electron effective Land? g factor in GaAs?Ga1?xAlxAs quantum wells and quantum-well wires under applied magnetic fields are studied within the effective-mass approximation. The interaction between the laser field and the semiconductor heterostructure is taken into account via a renormalization of the semiconductor energy gap and conduction-electron effective mass. Calculations are performed for the conduction-electron Land? factor and g-factor anisotropy by considering the non-parabolicity and anisotropy of the conduction band. Theoretical results are obtained as functions of the laser intensity, detuning and geometrical parameters of the low-dimensional semiconductor heterostructures, and indicate the possibility of manipulating and tuning the conduction-electron g factor in heterostructures by changing the detuning and laser-field intensity.

The hydrostatic-pressure effects on the electron-effective Lande factor and g-factor anisotropy in semiconductor GaAs–Ga1−xAlxAs quantum wells under magnetic fields are studied. The factor is computed by considering the non-parabolicity and anisotropy of the conduction band through the Ogg–McCombe effective Hamiltonian, and numerical results are displayed as functions of the applied hydrostatic pressure, magnetic fields, and quantum-well widths. Good agreement between theoretical results and experimental measurements in GaAs–(Ga, Al)As quantum wells for the electron g factor and g-factor anisotropy at low values of the applied magnetic field and in the absence of hydrostatic pressure is obtained. Present results open up new possibilities for manipulating the electron-effective g factor in semiconductor heterostructures.

The effects of the Dresselhaus spin splitting on the Lande g factor associated with conduction electrons in GaAs–(Ga,Al)As quantum wells are studied by using the nonparabolic Ogg–McCombe effective Hamiltonian. The g factor and cyclotron effective mass are calculated as functions of applied magnetic fields (along both the growth and in-plane directions) and GaAs well widths of the heterostructure. Present calculations indicate that in GaAs–(Ga,Al)As heterostructures, the inclusion of the Dresselhaus term leads to very small corrections in the effective Lande factor. Taking into account the effects of nonparabolic and anisotropic terms in the Hamiltonian is fundamental in obtaining quantitative agreement with experimental measurements. Moreover, the present results suggest that previous theoretical work on the Dresselhaus spin-splitting effects on the effective Lande factor should be viewed with caution if nonparabolic and anisotropic effects are not taken into account.

The effects of confinement and magnetic fields on the effective electron Land? g factor of GaAs?Ga1?xAlxAs cylindrical quantum well wires are studied. Calculations were carried out via the Ogg?McCombe effective Hamiltonian which is used to describe the non-parabolicity and anisotropy effects on the electron states in the conduction band. The applied magnetic field is taken along the wire axis, and the Schr?dinger equation corresponding to electron spin projections parallel and antiparallel to the magnetic field is solved by using an expansion of the electron wavefunctions in terms of two-dimensional harmonic oscillator wavefunctions. Calculations for the electron factor in GaAs?Ga1?xAlxAs cylindrical quantum well wires are compared with results from previous theoretical work. Moreover, the present results clearly indicate the importance of taking into account the non-parabolicity/anisotropy of the conduction band if one is interested in a quantitative understanding of the electron g factor in GaAs?Ga1?xAlxAs quantum well wires.

The effects of hydrostatic pressure and growth-direction applied magnetic fields on the exciton dispersion and in-plane effective mass in coupled GaAs–(Ga, Al)As quantum wells are investigated. Calculations for spatially direct and indirect excitons were performed within the variational procedure in the effective-mass and nondegenerate parabolic band approximations and by taking into account the coupling between the exciton centre-of-mass momentum and its internal structure. The pressure coefficient is also obtained as a function of both the hydrostatic pressure and growth-direction applied magnetic field.

A theoretical study of the growth-direction magnetic-field effects on the exciton photoluminescence peak energies in GaAs–Ga1−xAlxAs quantum-dot/ultrathin quantum-well systems is presented. Calculations are performed within the effective-mass approximation and taking into account nonparabolicity effects for both the conduction-band and valence-band effective masses. We use a simple 'QD+ultrathin QW' model heterostructure to mimic the actual physical system, and calculated results for the exciton diamagnetic shifts are found in overall agreement with recent experimental measurements.

We have performed a theoretical study of the cyclotron effective mass and electron effective Lande g‖ factor in semiconductor GaAs–Ga1−xAlxAs quantum wells under an applied magnetic field parallel to the growth direction of the quantum well. The theoretical approach is within the nonparabolic and effective-mass approximation and via an Ogg-McCombe effective Hamiltonian [Proc. Phys. Soc. London 89, 431 (1969); Phys. Rev. 181, 1206 (1969)] for the electron in the conduction band of the GaAs–Ga1−xAlxAs heterostructure, which allows a unified treatment of both the cyclotron mass and g‖ factor. Calculations are performed for different widths of the GaAs–Ga1−xAlxAs quantum wells and as functions of the applied magnetic field, with results in very good agreement with reported experimental measurements of the electron cyclotron effective mass and g‖ factor.

A quantum-mechanical calculation of radiative recombination in GaAs-(Ga, Al)As quantum wells and quantum-well wires, excited by a cw laser in a photoluminescence experiment under quasistationary excitation conditions, is perfomed. We work within the effective-mass approximation and the parabolic-band model for describing both electrons and holes, and consider, in the steady state, the interband absorption, and some radiative recombination mechanisms, such as recombination of electrons with free holes and with holes bound at acceptors, and nonradiative recombination involving traps. Carrier densities, chemical potentials, and electron-hole recombination decay times are calculated as functions of the temperature and laser intensity. Theoretical results are in good agreement with available experimental data.

The energy spectra of shallow donors and acceptors in GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As quantum-well structures have been calculated. The binding energies of the impurities were obtained within a variational calculation in the effective-mass approximation. Calculations were performed for simple neutral and double singly ionized impurities as functions of the position of the impurity in a GaAs quantum well of infinite depth and for various slab thicknesses. The effect of the spatially dependent screening is modeled with a dielectric response of the form ${\ensuremath{\epsilon}}^{\mathrm{\ensuremath{-}}1}$(r)=${\ensuremath{\epsilon}}_{0}^{\mathrm{\ensuremath{-}}1}$+(1-${\ensuremath{\epsilon}}_{0}$ $^{\mathrm{\ensuremath{-}}1}$)${e}^{\mathrm{\ensuremath{-}}r/a}$, with a screening parameter a\ensuremath{\approxeq}1.1 a.u. characteristic of bulk GaAs. Results are compared with Bastard's theory, which is based on a constant-${\ensuremath{\epsilon}}_{0}$ screening, and it is found that spatially dependent screening effects are small for donors down to very thin slab thicknesses, but can be quite important for all acceptors in GaAs quantum wells over a large range of slab thicknesses. Calculated results with improved statistics are in quantitative agreement with experimental data on neutral donors and acceptors.

The electronic structure of the interstitial hydrogen atom in alkaline-earth fluorides has been studied using the self-consistent-field multiple-scattering ${X}_{\ensuremath{\alpha}}$ method. In the calculations we have used a cluster constituted by the hydrogen atom and its first anion and cation neighbors. The contact parameters with the proton and the fluorine nuclei have been evaluated. The agreement obtained with the experimental results is in general good and indicates that this method is also appropriate to study defects in ionic crystals.

A model for the microscopic dielectric response ϵG,G′(q) of a covalent semiconductor is proposed in which the effects of the localized and plane wave features of the band structure on the polarizability are separated. Within this model for diamond a calculation is performed of the static longitudinal wave vector dependent macroscopic dielectric function ϵM(q), including local field corrections, together with an analysis in real space of the microscopic local field E(r) and polarization charge density ϱindr) induced by a uniform externally applied electric field. The results indicate that although the macroscopic dielectric function is essentially insensitive with respect to small changes in the effective charge model parameter Z, microscopic quantities such as the induced charge density and microscopic local field can be fairly sensitive to variations in Z. This suggests that careful tests on model based dielectric responses ϵG,G′(q) are probably necessary before one calculates, for instance, phonon frequencies. Cet article se preoccupe de la polarisabilite d'un semiconducteur covalent. On propose un modele pour la matrice dielectrique au niveau microscopique, symboliquement ϵG,G′(q), qui depend aussi d'un parametre de charge effectif, Z. On a choisi comme example le diamant, et on a calcule, avec la correction de champ local, la fonction dielectrique, ϵM(q), du niveau macroscopique. Lechamp electrique,E(r), etla densite de charge, ϱind(r), les deux au niveau microscopique, sont aussi calcules dans l'espace reel dans le cas particulier d'un champ electrique constant, impose de I'exterieur. Les resultats de cette analyse suggerent, que, bien que la fonction niacroscopique ϵM(q) est essentiellement insensible aux variations du parametre Z, les variables microscopiques, tels que la densite de charge et le champ electrique, peuvent en etre tres sensibles. Ceci suggere qu'il faut des experiences tres soignees si on veut utiliser des modeles pour la matrice dielectriqne pour determiner des quantites microscopiques, telles que les frbquences des phonons.

Considers the dielectric response matrix epsilon K,G(q, omega ) for silicon within a modified dynamic Johnson model (1974). The effect of inclusion of local microscopic fields in the dispersion of the volume plasmon of silicon is studied along the (100) direction up to the critical wavevector qc approximately=1.2 AA-1 and the results are compared with recent experimental work.

The self-consistent-field multiple-scattering method in the $X\ensuremath{\alpha}$ approximation is used to calculate the electronic structure and the optical transition energies of the $U$ center in Ca${\mathrm{F}}_{2}$, Sr${\mathrm{F}}_{2}$, and Ba${\mathrm{F}}_{2}$.

The SCF-MSXα method is applied in the study of the electronic structure of F centers in CaF2, SrF2, and BaF2. The predicted optical transition energies are in disagreement with the experimental data. An explanation for the discrepancy is provided showing the inadequacy of the spherical averaging of the potential within the muffin-tin approximation. La methode SCF-MSXα a ete utilisee pour la determination de la structure electronique des centres F dans CaF2, SrF2 et BaF2. Les energies calculees pour les transitions optiques sont en desaccord avec les resultats experimentaux. Une interpretation de ce desaccord a ete fournie montrant que la moyenne spherique du potentiel dans l'approximation “muffin-tin” n'est pas adequate en ce cas.

The binding energies of D/sup -/ states in P- and As-doped silicon crystals are calculated as functions of uniaxial compressive stress along the (100) direction within a variational scheme in the effective-mass approximation and with a Chandrasekhar-type variational function. A model Hamiltonian which takes into account valley-orbit corrections, electron-electron interaction, and stress effects is proposed. Our calculation shows that as the stress is applied, the outer electron orbital is driven readily into the two stress-deepened valleys, which leads to a strong decrease in the D/sup -/ binding energy. With further increase in stress, the inner electron orbital changes gradually from a function almost evenly distributed among the six conduction valleys into one in which the two stress-deepened valleys are dominant, and the D/sup -/ binding energy increases. Our results agree qualitatively with previous theoretical calculations and are in good agreement with far-infrared photoconductivity measurements in Si:P.

The effects of compressive uniaxial stress along the [111] direction and of valley-orbit corrections on the binding energies of D− states in Sb- and P-doped germanium are calculated. A variational procedure is used with a Chandrasekhar-type of variational wave function. The model Hamiltonian takes into account electron-electron interaction, valley-orbit corrections, and stress effects. The results show similar behavior as in previous work on doped silicon and quantitatively agree with available long-wavelength photoconductivity measurements for doped germanium. Der Einflus einachsigen Drucks in [111]-Richtung und von Tal-Bahn-Korrekturen auf die Bindungsenergien von D−-Zustanden in Sb- und P-dotiertem Germanium wird berechnet. Eine Variationsmethode zusammen mit einer Chandrasekhar-artiger Versuchswellenfunktion wird angewandt. Elektron-Elektron-Wechselwirkung, Tal-Bahn-Korrekturen und Druckeffekte werden im Modellhamiltonian mit einbezogen. Die Resultate weisen ein ahnliches Verhalten auf wie vorige Arbeiten an dotiertem Silizium, sie stimmen auch verhaltnismasig gut mit zur Verfugung stehenden Photowiderstandsmessungen im Langwellenbereich uberein.

The nearly free-electron self-consistent-field pseudopotential theory is used to analytically evaluate the dielectric function epsilon (k, omega ) for the alkali metals Li, Na and K, the effects of the crystal potential being included up to second order in the UG pseudopotential form factor, in the high-frequency limit. The plasmon dispersion omega p(k) is then obtained from the strong peak position of the electron energy loss function. The results are compared with experiment for Li, Na and K, and for increasing mod k mod the discrepancies between the theoretical and experimental plasmon dispersion become noticeable because the calculated dispersion curve is too steep when compared with experiment. The anisotropy of the dispersion is also calculated and found to be rather small for Na and K, while for Li, which has a larger pseudopotential coefficient, the plasmon anisotropy can be quite considerable for large values of mod k mod and should be noticeable experimentally.

A two-band model, which previously was used successfully to evaluate the optical absorption in A1, is applied to derive the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$- and $\ensuremath{\omega}$-dependent dielectric function ${\ensuremath{\epsilon}}_{M}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}},\ensuremath{\omega})$ for $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ parallel to the [100] direction with use of degenerate perturbation theory. Within the nearly-free-electron approximation, it is shown that a pair of (200) Bragg planes gives rise to another pole in the energy-loss function $\mathrm{Im}[\frac{\ensuremath{-}1}{\ensuremath{\epsilon}}]$ and hence to a collective mode. Both the dispersion of the mode throughout the first Brillouin zone and the strength of the mode are evaluated and are found to agree very well with electron-energy-loss spectroscopy data. A detailed discussion of the nature of this mode is given. The mode is of the same origin as the so-called zone-boundary collective state (ZBCS) first proposed by Foo and Hopfield in Na. Comparison is made with a numerical calculation of ${\ensuremath{\epsilon}}_{M}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}},\ensuremath{\omega})$ by Singhal for some discrete $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}$ values. The general importance of the ZBCS for the understanding of the energy-loss spectrum and for more complicated systems is pointed out.

Anisotropic structures in the inelastic-scattering cross section of x rays from single-crystal Li and of fast electrons from single-crystal Na and Al are found to arise from zone-boundary collective states (ZBCS) that, in contrast to the classical plasmon, depend strongly on the symmetry and on the strength of the crystal potential. We show that within the random-phase approximation (RPA), a nearly-free-electron-like two-band model is able to describe these states existing for q along various high-symmetry directions of the crystal. In Li in particular, a 〈200〉 ZBCS appears as a continuation of the plasmon beyond the cutoff wave vector ${q}_{c}$. For many years structures in this (q,\ensuremath{\omega}) regime have been associated with correlation effects beyond the RPA. Furthermore, due to the high sensitivity on the crystal potential, measured ZBCS's yield valuable information on the band structure, which are currently intensively studied by angularly resolved photoemission.

The nearly-free-electron pseudopotential theory is used to calculate the macroscopic dielectric function e(O, ω) for Li, Na, and K in the long-wavelength limit within the self-consistent-field approximation. The plasmon energies are obtained from the peak position of the energy loss function Im [–1/e(O, ω)]. The results are compared with the experiment and the agreement is good provided that the effects of ion-core polarization in the long-wavelength plasmon energy are taken into account. La theorie du pseudo-potentiel quant a l'approximation de l'electron presque libre est utilisee dans le calcul de la fonction dielectrique macroscopique e(O, ω) pour Li, Na et K dans la limite des longueurs d'onde longue et aussi dans l'approximation du champ auto-consistant. Les energies des plasmons sont obtenues a partir de la position du maximum de la fonction en perte d'energie Im [–1/e(O, ω)]. Les resultats sont compares a l'experience et la correspondance est bonne a partir du moment ou les effets de polarisation ion-coeur sont pris en consideration dans le calcul de l'energie du plasmon et dans la limite de longueur d'onde longue.

Anisotropic structures in the inelastic scattering cross-section of x-rays from single crystal Li and of fast electrons from single crystal Na are found to arise from zone boundary collective states (ZBCS), whose properties depend crucially on the symmetry and on the strength of the crystal potential. These ZBCSs are important in discussing various many-body effects. For Na the 110-ZBCS is consistent with a NFE band structure. This contrasts with the reduced bandwidth observed in photoemission and believed to be caused by many-body effects beyond the RPA. In Li a 200-ZBCS falls into a (q, ω) regime beyond the plasmon where structures have been associated with short-range correlations.

A theoretical study of the photoluminescence spectra associated with shallow acceptors in a GaAs‐(Ga,Al)As quantum well is performed. It is shown that an analysis of the acceptor‐photoluminescence line shape could allow an experimental determination of the quasi‐Fermi energy level of the conduction‐subband‐electron gas as well as of the on‐edge acceptor binding energy.

Quasi-periodic GaAs-(Ga,Al)As Fibonacci superlattices under in-plane magnetic fields are studied within the effective-mass approximation. Electron-envelope wavefunctions, magnetic subbands and intraband transition strengths are obtained using a parabolic model for the conduction band, and via an expansion in harmonic-oscillator wavefunctions. Calculations are performed for magnetic fields related by integer powers of the golden mean tau =(1+512/)/2. It is shown that, for magnetic field values scaled by tau 2n, the corresponding magnetic levels, electron wavefunctions and transition strengths essentially exhibit a self-similar or anti-self-similar behaviour as appropriate for a GaAs-(Ga,Al)As Fibonacci superlattice. Also, for a given magnetic field, the interband transition strengths have similar properties to those found for the case of periodic superlattices. The intraband absorption coefficients are calculated for magnetic field values scaled by tau 2n, and theoretical absorption spectra, when properly scaled, are shown to be self-similar (for even n) or anti-self-similar (for odd n), a result which could be experimentally verified in n-doped GaAs-(Ga,Al)As Fibonacci superlattices.