The Rashba effect on a double-barrier spin polarizer is considered using a formalism that produces accurate results with little computational effort. In previous articles, we proposed a spin polarizer consisting of a well made of a dilute... more
The Rashba effect on a double-barrier spin polarizer is considered using a formalism that produces accurate results with little computational effort. In previous articles, we proposed a spin polarizer consisting of a well made of a dilute magnetic semiconductor (DMS) enclosed by two non-magnetic barriers. In the absence of Rashba effect, the magnetization of the well produces totally polarized electronic levels separated by 0.150.15 eV. The highest steady magnetic field obtained in a laboratory could not produce a Zeeman splitting so big. As a consequence the calculated currents are almost totally polarized. The Rashba spin–orbit Hamiltonian produces a spin flip. Therefore, the levels at the well have not well-defined spin polarization and the currents are less polarized. The device presented here would be useful for spintronics because there are DMS ferromagnetic at room temperature. Our tight-binding Hamiltonian, including the Rashba term, isBy using a decimation formalism, all these terms are treated exactly. Finally, the Rashba term HRHR is very small. Therefore, it is treated using second order perturbation theory. The calculation confirm that the Rashba effect on the currents is of second order. Consequently, the resulting depolarization is very small.
Research Interests: Condensed Matter Physics, Quantum Physics, Spintronics, Magnetic field, Nanostructures, and 12 moreSpin-Orbit Coupling, Second Order, Room Temperature, Kinetic Energy, Tight Binding, Electric Field, Charge Distribution, Mean Field Approximation, Perturbation Theory, Spin Orbit Coupling, Spin Polarization, and Dilute magnetic semiconductor
Warning about jobs in Brazil. [Physics Today 33, 92 (1980)]. Edward Siegel, Ivan C. da Cunha Lima. Keywords. Careers in physics and science. Science and society.
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Warning about jobs in Brazil. [Physics Today 33, 92 (1980)]. Edward Siegel, Ivan C. da Cunha Lima. Keywords. Careers in physics and science. Science and society.
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Impurity bands were investigated further in order to show how sensitive the resistivity is in n-type doped semiconductors to changes in electron correlation. The effect of correlation as well as overlap on the electron hopping energy... more
Impurity bands were investigated further in order to show how sensitive the resistivity is in n-type doped semiconductors to changes in electron correlation. The effect of correlation as well as overlap on the electron hopping energy integral are taken into account via Heitler-London two particle wave functions. The magnitude of the electron hopping energy integral is reduced. The electron correlation substantially reduces the bandwidth via the cut off of the long range hopping. The impurity level tends to the ionization energy = - 1.0 as Rij yields infinity. The calculated resistivities for Si:P, Ge:Sb and CdS:In when compared to the experimental data present good agreement around and above the impurity critical concentration for the metal-nonmetal transition. The comparison with AMO-MT calculation shows a big enhancement due to a stronger electron correlation.
The recent HL-MT scheme for electric conduction in doped semiconductors is investigated by including the effect of impurity correlation. The impurity resistivities of Si:P and CdS:In are calculated. It is found that the resistivity is... more
The recent HL-MT scheme for electric conduction in doped semiconductors is investigated by including the effect of impurity correlation. The impurity resistivities of Si:P and CdS:In are calculated. It is found that the resistivity is enhanced by electron correlation and quenched by impurity correlation.
The behavior of impurity in semiconductors is investigated via the electron transfer energy integral. The resistivity of Ge:Sb is calculated for various types of transfer integral and compared with the experimental results. Neglecting... more
The behavior of impurity in semiconductors is investigated via the electron transfer energy integral. The resistivity of Ge:Sb is calculated for various types of transfer integral and compared with the experimental results. Neglecting localization effects, the variation of the energy gap Ag between impurity bands is compared with the experimental activation energy e2 of Si:P and Ge:Sb, for different concentrations. A qualitative agreement with the experiment has been found.
A previously developed self-consistent many body theory for disordered systems was applied to calculate the paramagnetic susceptibility of phosphorus doped silicon. The results at 0 K are compared with the experimental results at low... more
A previously developed self-consistent many body theory for disordered systems was applied to calculate the paramagnetic susceptibility of phosphorus doped silicon. The results at 0 K are compared with the experimental results at low temperature and other calculations. A reasonable agreement with the experiment was found concerning the critical concentration of the impurities when the metal non-metal transition occurs.
The Ghatak and Sherrington theory for an Ising spin glass was extended for random anisotropy. The susceptibility and specific heat were calculated using a Gaussian distribution of probability for the magnitude of the random anisotropy.... more
The Ghatak and Sherrington theory for an Ising spin glass was extended for random anisotropy. The susceptibility and specific heat were calculated using a Gaussian distribution of probability for the magnitude of the random anisotropy. This effect shows a cusp in the susceptibility but not in the specific heat.
The density of states for electrons at the inversion layer of an MOS structure due to Na(+) impurities located in the oxide was obtained. The impurity potential is assumed unscreened. The disorder was taken into account to obtain the... more
The density of states for electrons at the inversion layer of an MOS structure due to Na(+) impurities located in the oxide was obtained. The impurity potential is assumed unscreened. The disorder was taken into account to obtain the configurational averaged Green's function starting from a tight binding Hamiltonian.
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ABSTRACT The magnetic order resulting from an indirect exchange between magnetic moments provided by spin-polarized hole gas in the metallic phase of a GaMnAs double layer structure is studied via Monte Carlo simulation. The coupling... more
ABSTRACT The magnetic order resulting from an indirect exchange between magnetic moments provided by spin-polarized hole gas in the metallic phase of a GaMnAs double layer structure is studied via Monte Carlo simulation. The coupling mechanism involves a perturbative calculation in second order of the interaction between the magnetic moments and carriers (holes). We take into account a possible polarization of the hole gas due to the existence of an average magnetization in the magnetic layers, establishing, in this way, a self-consistency between the magnetic order and the electronic structure. That interaction leads to an internal ferromagnetic order inside each layer, and a parallel arrangement between their magnetizations, even in the case of thin layers. This fact is analyzed in terms of the inter- and intra-layer interactions. Comment: 17 pages and 14 figures
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ABSTRACT The recent theory of Ferreira da Silva et al. for the specific heat of doped semiconductors, described by the Hubbard model with a random-transfer integral, has been studied in the presence of a magnetic field and impurity... more
ABSTRACT The recent theory of Ferreira da Silva et al. for the specific heat of doped semiconductors, described by the Hubbard model with a random-transfer integral, has been studied in the presence of a magnetic field and impurity correlations, incorporated through a hard-core pair-correlation function. The low-temperature specific heat and the zero-temperature susceptibility of uncompensated phosphorus-doped silicon have been calculated as a function of the impurity concentration. It is found that both electron and impurity correlations enhance the susceptibility and quench the specific heat. The behavior of the relative change in the specific heat due to the magnetic field agrees qualitatively with the low-temperature experimental results.
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ABSTRACT The density of states for electrons bound to Na+ impurities inside the inversion layer at the semiconductor-insulator interface of an MOS structure is calculated as a function of impurity concentration. The impurity potential is... more
ABSTRACT The density of states for electrons bound to Na+ impurities inside the inversion layer at the semiconductor-insulator interface of an MOS structure is calculated as a function of impurity concentration. The impurity potential is considered unscreened and the electrical quantum limit is assumed. A simple one-electron Hamiltonian is used and the disorder is treated through a cluster calculation. It is shown that the impurity band has a considerable bandwidth for impurity concentrations in a range of the experimental regime (this result agrees with the experimental findings of Hartstein and Fowler), and that the upper Hubbard band stands well above the lower band at very low concentration (in rough agreement with recent calculation done by Phelps and Bajaj on D− state).
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The binding energy of electrons to shallow donors in GaAs/AlAs quantum wells in the vicinity of the type-I to type-II transition is obtained for impurities lying inside the GaAs layer. The calculation is performed variationally using a... more
The binding energy of electrons to shallow donors in GaAs/AlAs quantum wells in the vicinity of the type-I to type-II transition is obtained for impurities lying inside the GaAs layer. The calculation is performed variationally using a two-parameter trial function, the same for both type-I and type-II structures. The transition occurs for a GaAs layer width near 37 Å. For widths smaller than 37 Å we obtain the binding energy for the X electrons in a GaAs/AlAs double well, where the impurity lies inside the GaAs middle barrier. For widths larger than 37 Å the binding energy is calculated using a single well for the Gamma electrons. A change of symmetry from s-like to p-like is obtained as the transition occurs, for the Gamma and for the X electron, respectively.
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We calculate the density of states (DOS) for Na+ impurity bands in n-type Si/Sio2 metal-oxide- semiconductor structures with a Hubbard-type model and using as a basis Martin and Wallis single-impurity states. We show that the intrasite... more
We calculate the density of states (DOS) for Na+ impurity bands in n-type Si/Sio2 metal-oxide- semiconductor structures with a Hubbard-type model and using as a basis Martin and Wallis single-impurity states. We show that the intrasite correlation energy increases with the applied electric field on the junction. The same occurs with the bandwidth and with the energy corresponding to the
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In this work, we have investigated the behavior of the line shape of the cyclotron resonance for a two-dimensional electron gas interacting with longitudinal-surface-acoustical phonons, in the presence of a strong magnetic field. The... more
In this work, we have investigated the behavior of the line shape of the cyclotron resonance for a two-dimensional electron gas interacting with longitudinal-surface-acoustical phonons, in the presence of a strong magnetic field. The magnetophonon conductivity is evaluated in terms of the dissipative and reactive effects on the electron gas, using the memory-function formalism. New results for both temperature and magnetic field dependences of the cyclotron resonance are studied and compared with conflicting points of previous works. Besides, it is shown that a splitting on the dynamical conductivity peak should always be expected for magnetic fields lower than the corresponding one to the quantum limit, i.e., with only the first Landau level occupied, in agreement with what has been found experimentally.
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ABSTRACT The advances in nanofabrication and in tunneling detection currently allows the observation of jumps of a single electron between islands. In this work we study the electron tunneling between two quantum well wires (TQWW) by... more
ABSTRACT The advances in nanofabrication and in tunneling detection currently allows the observation of jumps of a single electron between islands. In this work we study the electron tunneling between two quantum well wires (TQWW) by solving the time dependent Schrödinger equation using a diagrammatic perturbative technique. In order to get a realistic confining potential and electronic density, the Schrödinger and the Poisson equations have been solved selfconsistently for several system sizes. We start preparing the system such that an electron occupy only one of the wires. The time evolution of its average position is calculated and the charge density is obtained at regular time intervals, monitoring, in this way, the dynamics of the electron in the TQWW. It is observed that, depending on the architecture of the system, after the electron can be found in a different wire.
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... I. C. da Cunha Lima, A. Ferreira da Silva, P. S. Guimaraes, L. F.Perondi, and J. R. Senna Instituto de Pesquisas Espaciais, Conselho Nacional de Desenvolvimento ... To obtain the density of states, we attempt to calculate the... more
... I. C. da Cunha Lima, A. Ferreira da Silva, P. S. Guimaraes, L. F.Perondi, and J. R. Senna Instituto de Pesquisas Espaciais, Conselho Nacional de Desenvolvimento ... To obtain the density of states, we attempt to calculate the Green's function for the above Hamiltonian in a ...
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The eigenenergies of the hydrogen molecule are calculated in the alternant-molecular-orbital approximation. Emphasis is given to two-dimensional (2D) systems. Results for the 2D and 3D cases are compared and also with the singlet state of... more
The eigenenergies of the hydrogen molecule are calculated in the alternant-molecular-orbital approximation. Emphasis is given to two-dimensional (2D) systems. Results for the 2D and 3D cases are compared and also with the singlet state of the variational Heitler-London approximation. Unlike what is observed in 3D, in 2D we found that in the ground-state electrons are highly correlated and that double occupancy is inhibited.
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A previously developed theory for electronic properties of doped semiconductors that uses a Hubbard-like Hamiltonian and takes into account the effect of disorder is applied to the impurity bands associated with inversion layers. It is... more
A previously developed theory for electronic properties of doped semiconductors that uses a Hubbard-like Hamiltonian and takes into account the effect of disorder is applied to the impurity bands associated with inversion layers. It is shown that the impurity bands have a considerable bandwidth for concentrations in a range of experimental findings.
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Carrier-mediated magnetism in semiconductors shows important and potentially useful differences from magnetism in metals [1] such as light-or bias-controlled ferromagnetism [2-3]. Motivated by experiments reporting in GaAs quantum wells... more
Carrier-mediated magnetism in semiconductors shows important and potentially useful differences from magnetism in metals [1] such as light-or bias-controlled ferromagnetism [2-3]. Motivated by experiments reporting in GaAs quantum wells (QWs) with Mn-delta ...
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ABSTRACT A model for b.c.c. metals is proposed by adding electron-ion interaction term from Krebs' model to the ion-ion interaction term of axially symmetric model of Lehman et al. The computed phonon frequencies of sodium are... more
ABSTRACT A model for b.c.c. metals is proposed by adding electron-ion interaction term from Krebs' model to the ion-ion interaction term of axially symmetric model of Lehman et al. The computed phonon frequencies of sodium are found to reproduce experimental ones within the limit of experimental error.RésuméOn propose Un modèle pour les metaux cubique b.c.c. corps centre dans lequal ou tient compte du terme d'interaction electron-ion du model de Krebs et du terme d'interaction ion-ion du modèle de symétrie axiale de Lehman et al. Les fréquences phonon du sodium calculées coincident dans les limites d'erreurs experimentales avec les frequences presurées.
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ABSTRACT The indirect interaction between two magnetic impurities in a double quantum well under a strong electric field perpendicular to the interfaces is obtained as a function of the field strength and the barrier width. We show that,... more
ABSTRACT The indirect interaction between two magnetic impurities in a double quantum well under a strong electric field perpendicular to the interfaces is obtained as a function of the field strength and the barrier width. We show that, if a single state is bound to the well, the exchange energy factorizes as a form factor depending on the quantum well structural parameters and a two-dimensional RKKY interaction. We obtained a fast decrease of the exchange with the barrier width for the impurities lying in different wells.
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... For the sake of simplicity we will briefly outline the HLMT scheme, while the reader should refer to the orig inal works for details. ... Chem. Solids 6 (1958) 69. [2] EA Davis and WD Compton, Phys. Rev. 140 (1965) A2183; C.... more
... For the sake of simplicity we will briefly outline the HLMT scheme, while the reader should refer to the orig inal works for details. ... Chem. Solids 6 (1958) 69. [2] EA Davis and WD Compton, Phys. Rev. 140 (1965) A2183; C. Yamanouchi, K. Mizuguchi and W. Sasaki, J. Phys. Soc. ...
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ABSTRACT We use Monte Carlo simulations to analyze electric-field control of Curie temperature TC for carrier-mediated ferromagnetism in semiconductors. Gating employed to achieve electrostatic doping in an optimized geometry of (Ga,... more
ABSTRACT We use Monte Carlo simulations to analyze electric-field control of Curie temperature TC for carrier-mediated ferromagnetism in semiconductors. Gating employed to achieve electrostatic doping in an optimized geometry of (Ga, Mn)As, a prototypical ferromagnetic semiconductor, reveals a highly tunable ferromagnetic order. We show the feasibility of ΔTC>100 K, an order of magnitude greater then the state-of-the-art measurements, at fields substantially smaller then the breakdown values. Such controllable ferromagnetism may help elucidate the mechanism of carrier-mediated magnetism in various semiconductors and offer versatile spintronic applications.
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We calculate the ground-state energies of muonic molecules formed by deuterium-deuterium, tritium-tritium, and deuterium-tritium nuclei plus a negative muon confined in a two-dimensional (2D) region. We show that the equilibrium distance... more
We calculate the ground-state energies of muonic molecules formed by deuterium-deuterium, tritium-tritium, and deuterium-tritium nuclei plus a negative muon confined in a two-dimensional (2D) region. We show that the equilibrium distance between nuclei is a factor of 4 smaller and the vibrational energies are about a factor of 5 higher than the corresponding three-dimensional (3D) muonic molecules, thus favoring fusion reactions. In fact, the estimated d+t fusion rate is found to be three orders of magnitude higher in 2D than in 3D.
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In this work we present results for the transport properties of a spin polarizer consisting of a resonant tunneling diode (RTD) in which the well is made of Ga1-xMnxAs. This is a diluted magnetic semiconductor (DMS) of p type.The... more
In this work we present results for the transport properties of a spin polarizer consisting of a resonant tunneling diode (RTD) in which the well is made of Ga1-xMnxAs. This is a diluted magnetic semiconductor (DMS) of p type.The magnetization of the well produces a splitting of the valence band of approximately 0.15eV and consequently a splitting of resonant peaks. This 0.15eV separation is bigger than the one produced by the highest stationary magnetic field obtained in a laboratory. As a consequence we get a spin polarized current when only one of these peaks is in between the Fermi level and the top of the valence band. We have considered heavy hole (HH) and light hole (LH) bands. The last one had not been considered in our previous works.Our system is described by a tight-binding Hamiltonian. The carriers interaction is calculated in the Hartree approximation. The charge distribution of the system and the potential profile are calculated self-consistently.Our results show that the system works as a very efficient spin filter. The magnetism and charge neutrality is mainly due to heavy holes. For a system with wide barriers, the spin polarized current is mainly due to light holes.
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ABSTRACT We investigate the spin-polarized transport of holes in GaMnAs/GaAs heterostructures with Mn concentration 5% in which a ferromagnetic order is known to exist. Disorder enters the problem both in the random distribution of Mn... more
ABSTRACT We investigate the spin-polarized transport of holes in GaMnAs/GaAs heterostructures with Mn concentration 5% in which a ferromagnetic order is known to exist. Disorder enters the problem both in the random distribution of Mn centers and impurities, and also in the orientation of the magnetic moments at the Mn sites. We take into account the existence of an impurity band determining the extended or localized nature of the states at and near the Fermi level. Magnetic order and resistivity are inter-related due to the influence of the spin polarization of the impurity band and the effect of the Zeeman splitting on the mobility edge. We obtain two channels of transport, one provided by the extended states above the mobility edge, when this lies below the Fermi level, the other coming out of the thermal excitation of the localized states through a hopping mechanism. We discuss the competition between these two channels in determining, once having obtained the dependence of the resistance on temperature, the metallic or non-metallic nature of the sample.