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Item Cyclotron resonance of electrons in GaAs-Gal-x AIxAs heterojunctions(1989) Osorio, Francisco Aparecido Pinto; Degani, Marcos Henrique; Hipólito, OscarMostrar mais The cyclotron resonance mass of a quasi-two-dimensional polaron in GaAsGaA1As heterostructures and quantum wells is calculated. Experimental results recently obtained by different groups are well described in the magnetic quantum limit.Mostrar mais Item Electron-phonon effects on the ground impurity level in quasi-one-dimensional semiconductor heterostructures(1989) Osorio, Francisco Aparecido Pinto; Degani, Marcos Henrique; Hipólito, OscarMostrar mais We calculate the effects of the electron-phonon interaction on the binding energies of an impurity placed in a quantum-well wire of rectangular cross section and finite barrier potential to the confined electrons. The calculations are performed as a function of the size of the wire for different positions of the impurity and for several values of the heights of the barrier potential. The results show that the energies are almost the same in wires with comparable cross-sectional area.Mostrar mais Item Impurity-bound magnetopolaron in GaAs quantum well structures(1991) Osorio, Francisco Aparecido Pinto; Maialle, Marcelo Zoéga; Hipólito, OscarMostrar mais We report for the first time a theoretical calculation for the resonant donor-impurity magnetopolaron in GaAs - Ga1−χAlχAs quantum-well structures. The intra-donor ls → 2p+ transition frequencies are calculated as a function of the magnetic field, by taking into account the polaron effects and nonparabolicity of the conduction band. We found a pinning behavior due to interaction with LO phonons as suggested by the experimentalists. Our results for the peak positions of those transitions are in very good agreement with recent experimental data.Mostrar mais Item Magnetopolarons in quantum-well wires(1992) Wendler, L.; Chaplik, A.; Hipólito, Oscar; Osorio, Francisco Aparecido PintoMostrar mais The interaction of quasi-one-dimensional electrons and longitudinal-optical (LO) phonons, placed in a perpendicular magnetic field is calculated. Results are presented for the polaron correction to the Landau levels and the polaron cyclotron mass.Mostrar mais Item Effects of confinement on shallow impurities in GaAs-Ga1-xA1xAs quantum dots(1992) Osorio, Francisco Aparecido Pinto; Hipólito, Oscar; Peeters, Francois M.Mostrar mais The ground state energy of a shallow impurity placed in the center of a circular quantum dot is studied. The effects of the strength of the confinement potential and a perpendicular magnetic field are investigated theoretically.Mostrar mais Item Cyclotron resonance of interface polarons in sernicomductor heterostructures(1994) Osorio, Francisco Aparecido Pinto; Degani, Marcos Henrique; Hipólito, OscarMostrar mais Item Polaron effects on the impurity binding energy in quantum wires(1995) Osorio, Francisco Aparecido Pinto; Degani, Marcos Henrique; Hipólito, OscarMostrar mais We report a calculation of the electron-phonon interaction effects on donor impurity binding energy in a semiconductor quantum wire of rectangular cross section and finite barrier potential. The results for the binding energy are obtained as a function of the size of the wire for different positions of the impurity and for several values of the potential confining barrier height. It is found that the presence of phonons changes significantly the values of the impurity binding energies of the system.Mostrar mais Item Potential barrier height on the intrasubband and intersubband quasi-one dimensional plasmons(1997) Machado, Paulo César Miranda; Osorio, Francisco Aparecido Pinto; Borges, Antonio NewtonMostrar mais The effects of the potential barrier height on the collective excitations of a electron gas confined in a GaAs-AlxGa1-xAs quantum wire of rectangular cross-section are investigated theoretically. For several potential barrier heights, we calculated the plasmon energy, structure factor and pair-correlation function, within the Random-Phase Approximation regime, considering a three-subband model with only the lowest subband populated by electrons. We verified that the intersubband plasmon is more sensitive to the potential barrier height variation than the intrasubband plasmon. We also observed that the confining potential effect decreases with the increasing of the wire-width.Mostrar mais Item Collective excitation in G a A s − A l x Ga 1 − x As quantum wires: multisubband model(1997) Machado, Paulo César Miranda; Leite, Jose Roberto; Osorio, Francisco Aparecido Pinto; Borges, Antonio NewtonMostrar mais The effects of the potential barrier height on the collective excitations of an electron gas confined in a GaAs-Al xGa 12xAs quantum wire of rectangular cross section are investigated theoretically by using the self-consistent field approximation theory proposed by Singwi, Tosi, Land, and Sjo¨lander ~STLS! @Phys. Rev. 176, 589 ~1968!#. For several potential barrier heights, we calculated the effective potential, plasmon energy, structure factor, and pair-correlation function, considering a three-subband model with only the lowest subband populated by electrons. We verified that the intersubband plasmon is more sensitive to the potential barrier height variation than the intrasubband plasmon. We also observed that the confining potential effect decreases with the increasing of the wire width. The random-phase approximation results are also presented by comparison with the STLS results and significant differences were foundMostrar mais Item Polarizability of a donor impurity in a GaAs-AlGaAs quantum wire(1997) Osorio, Francisco Aparecido Pinto; Borges, Antonio Newton; Caparica, Álvaro de Almeida; Leite, Jose RobertoMostrar mais The polarizability and the ground state binding energy of a donor impurity located in a semiconductor quantum well wire of rectangular cross-section with finite barrier potential is calculated through the variational method. We assume that the donor is located at the center of the wire and that the electric field is applied in the direction perpendicular to the wire length (z-direction), making an angle θ with the x-axis. We present our results for the ground state binding energy as a function of the size of the wire for several values of the electric field strength and of the angle θ. It is found that the polarizabilities decrease as the wire dimensions (Lx and Ly) decrease, until they reach a minimum at a certain value of Lx (Ly fixed) and then increase as the width becomes smaller. The binding energies and the polarizabilities, as expected, have a strong dependence on the geometrical form of the wire and on the angle θ.Mostrar mais Item Solução da equação de Schrodinger independente do tempo para um poço de potencial quadrado assimétrico(1997-03) Machado, Paulo César Miranda; Osorio, Francisco Aparecido Pinto; Borges, Antonio NewtonMostrar mais Using a common theme in Quantum Mechanics, we reached an interesting result which is not usually developed in the traditional literature. This theme is the calculation of the electron energy eigenvalue in assymmetric nite square potential wells. We will show that the electron energy eigenvalue in assymmetric nite square potential wells may be obtained from rst and second classes solutions of symmetric nite square potential wells, which are found in Quantum Mechanics books.Mostrar mais Item Electron–optical-phonon interaction effect on the intradonor transition energies in doped GaAs−AlxGa1−xAs quantum wells(1998) Osorio, Francisco Aparecido Pinto; Maialle, Marcelo Zoéga; Hipólito, OscarMostrar mais We report a calculation of 1s→2p1 transition energies of a donor impurity magnetopolaron located in GaAs quantum wells in the presence of an external magnetic field. The impurity levels are obtained through a variational method by choosing a Gaussian trial wave function with only one variational parameter. Our theoretical results can account for the experimental data for the center-donor system when the approximation of a single well is used. We also found no evidence for the presence of electron–nonbulk-phonon interaction needed to understand this problem.Mostrar mais Item Short range correlation effects in a polaron gas in gaas-algaas quantum well wires(1999) Borges, Antonio Newton; Osorio, Francisco Aparecido Pinto; Machado, Paulo César Miranda; Hipólito, OscarMostrar mais We investigate the short-range correlation effects of plasmon–phonon collective excitations in a quantum well wire by using the self-consistent field approximation theory proposed by Singwi, Tosi, Land and Sjolander [Phys. Rev.176, 589 (1968)]. In our calculation model, we consider a three-subband model with only one populated, for a rectangular cross-section quantum well wire with infinite height for the potential barrier. We have verified that by decreasing the wire width (and/or decreasing the electronic density), the local field correction effects are increased. We compare the present results with those obtained within the Random Phase Approximation throughout the paper and found that the differences between the two calculation methods are more significant for the intrasubband plasmon.Mostrar mais Item Vanadium characterization in BTO: V sillenite crystals(1999) Carvalho, Jesiel Freitas; Franco, Roberto Weider de Assis; Magon, Claudio José; Nunes, Luiz Antonio de Oliveira; Pelegrini, Fernando; Hernandes, Antonio CarlosMostrar mais Visible and Infrared Optical Absorption and Electron Paramagnetic Resonance (EPR) techniques have been used to characterize the intrinsic defects in sillenite type crystals: nominally pure Bi12TiO20 (BTO) and doped with vanadium (BTO:V). Optical quality crystals, with the composition Bi12.04±0.08Ti0.76±0.07V0.16±0.02O20, have been grown. Results obtained by these different techniques have shown unambiguously the 5+ valence state of the vanadium ion in BTO:V crystals. In pure BTO samples, the EPR and optical spectra show strong evidence of the presence of the intrinsic defect BiM 3+ + ho +, which consists of a hole h+, mainly located on the oxygen neighbors of the tetrahedrally coordinated Bi3+ ion. After doping with vanadium, results have shown that the characteristic bands, associated to this hole defect center, disappear, suggesting its transformation in single Bi3+. Anisotropy of the EPR spectra , at 20 K, is related to Fe3+ impurities.Mostrar mais Item Cyclotron mass of electrons in gaas-algan heterostructures(1999-12) Oliveira, Solemar Silva; Souza, Márcio Adriano Rodrigues; Borges, Antonio Newton; Osorio, Francisco Aparecido PintoMostrar mais The quasi-two-dimensional electron cyclotron mass in GaN-AlxGa1xN heterostructures is theoret- ically calculated. The shifting in Landau Levels due to the electron Longitudinal Optical phonon interaction is calculated through the Second Order Improved Wigner Brillouin Perturbation Theory (IWBPT). Experimental results recently obtained for GaN heterojunction are well described by the theory. We have also investigated the e ects of the electronic density on the Cyclotron Resonance frequency.Mostrar mais Item Non-classical properties of even circular states(2000) Pereira, Regiane Aparecida Ragi; Baseia, Basílio; Mizrahi, Salomon SylvainMostrar mais Here we investigate some general properties of the so-called even circular state (ECS) produced in a cavity, consisting of a superposition of N coherent states |αk (k = 1, 2, . . . , N) with the same |αk |. Several special states may emerge from this kind of superposition: in particular, when 1 (e|αk |2/N)N 4N a Fock state with N quanta is produced, whereas when (e|αk |2/N)N 1 one gets a vacuum state. We analyse the atomic scattering the ECSs produce when two-level atoms go through the cavity and also the non-classical depth of these states.Mostrar mais Item Synthesis, crystal growth and characterization of γ-Phase bismuth titanium oxide with gallium(2000) Lobato, Arilson Reges; Lanfredi, Silvania; Carvalho, Jesiel Freitas; Hernandes, Antonio CarlosMostrar mais Gallium solubility in the Bi12TiO20 (BTO) matrix was investigated by solid state reaction synthesis and Bi12Ti(1-x)GaxO20 (BTGaO) single crystals were grown by Top Seeded Solution Growth (TSSG). We determined that it is possible to obtain a continuous solid solution from (x)Bi12TiO20:(1-x)Bi12[Ga0.7Bi0.3]O20andthatGareplacesTiintheBTOmatrixgivingBi12Ti(1-x)Ga(x)O20 up to x < 0.2. BTGaO single crystals grown with an excess of Bi2O3 were transparent, a bleaching effect was observed due to the presence of gallium in the crystalline sillenite structure and their lattice parameter was higher than for pure BTO. The results for BTGaO single crystals showed an increase in the optical activity from ρ0 = 6.4° ± 0.3°/mm, for BTO, to ρ0 = 9.7° ± 0.3°/mm, for BTGaO grown with x = 0.30 in the melt. The BTGaO crystal presented an activation energy value of 0.48 ± 0.02 eV for 100 °C ≤ T ≤ 300 °C.Mostrar mais Item Interpolation from number states to chaotic states of the electromagnetic field(2001) Baseia, Basílio; Duarte, Sérgio José Barbosa; Malbouisson, Jorge Mário CarvalhoMostrar mais We introduce new two-parameter states of the quantized radiation field interpolating from number states to chaotic states. Instead of dealing with pure states, we consider truncated mixtures of number states—number-chaotic states (NCS)—which reduce to number and chaotic (thermal) states in two well-defined limits. We study the statistical and squeezing properties of such states and show that there is a value of the chaoticity parameter ¯n at which a transition from sub- to super-Poissonian characteristics occurs. Analysing the atomic population inversion in the Jaynes–Cummings model for these NCSs, we demonstrate the appearance of collapses and revivals as ¯n is increased. Their phase space representations are studied emphasizing the changes as the parameters are varied and we discuss the nonclassical depth.Mostrar mais Item Critical densities for the rpa approach in quasi one dimensional electronic systems(2002) Borges, J. B.; Machado, Paulo César Miranda; Osorio, Francisco Aparecido Pinto; Borges, Antonio NewtonMostrar mais The intrasubband pair-correlation function, g(x), for a quasi-one-dimensional electron gas confined in a GaAs–AlxGa1—xAs rectangular quantum wire within the random-phase approximation (RPA) is calculated for several values of the potential barrier height and wire width. We have studied the dependence of the pair-correlation function on the electronic density, and delimited the regions where the RPA approach gives physically acceptable results, i.e. the electronic density values where g(x) possesses positive values for small interparticle separations. The critical density increases with increasing potential barrier height or decreasing wire width.Mostrar mais Item Zeeman effect in CdMnTe parabolic and half parabolic quantum wells(2002) Cunha, Jalles Franco Ribeiro da; Osorio, Francisco Aparecido Pinto; Borges, Antonio Newton; Souza, Márcio Adriano RodriguesMostrar mais We have investigated the electronic structure of Cd1xMnxTe parabolic quantum wells and half- parabolic quantum wells heterostructures in the envelope function approximation using the k p method. We have considered an external magnetic eld applied in two di erent con gurations: in the plane of the layer and in the growth direction. The con ned states have been calculated taking into account the e ective mass dependence of the Mn concentration and the strain e ects. In this work we analyze the giant Zeeman splitting due to applied magnetic elds and we have compared the energies of the excitonic transitions hh (lh) ! el for the magnetic eld in the two considered con gurations. Comparison of our results for the half-parabolic quantum wells with available experimental data is made.Mostrar mais