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Papers by Ivan da Cunha Lima
Physica B-condensed Matter, 2004
The Rashba effect on a double-barrier spin polarizer is considered using a formalism that produce... 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.
Phys Today, 1980
Warning about jobs in Brazil. [Physics Today 33, 92 (1980)]. Edward Siegel, Ivan C. da Cunha Lima... more 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.
Physics Today, 1980
Warning about jobs in Brazil. [Physics Today 33, 92 (1980)]. Edward Siegel, Ivan C. da Cunha Lima... more 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.
Modern Physics Letters B
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Modern Physics Letters B
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Modern Physics Letters B
ABSTRACT
Solid State Communications
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Physical Review B
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Physical Review B
ABSTRACT
Brazilian Journal of Physics
Impurity bands were investigated further in order to show how sensitive the resistivity is in n-t... 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 includ... 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 integ... 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 cal... 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... 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(+) impur... 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.
Physical Review B, 2003
ABSTRACT The magnetic order resulting from an indirect exchange between magnetic moments provided... 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
Physical Review B, 1982
ABSTRACT The recent theory of Ferreira da Silva et al. for the specific heat of doped semiconduct... 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.
Physical Review B, 1981
ABSTRACT
Physica B-condensed Matter, 2004
The Rashba effect on a double-barrier spin polarizer is considered using a formalism that produce... 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.
Phys Today, 1980
Warning about jobs in Brazil. [Physics Today 33, 92 (1980)]. Edward Siegel, Ivan C. da Cunha Lima... more 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.
Physics Today, 1980
Warning about jobs in Brazil. [Physics Today 33, 92 (1980)]. Edward Siegel, Ivan C. da Cunha Lima... more 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.
Modern Physics Letters B
ABSTRACT
Modern Physics Letters B
ABSTRACT
Modern Physics Letters B
ABSTRACT
Solid State Communications
ABSTRACT
Physical Review B
ABSTRACT
Physical Review B
ABSTRACT
Brazilian Journal of Physics
Impurity bands were investigated further in order to show how sensitive the resistivity is in n-t... 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 includ... 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 integ... 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 cal... 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... 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(+) impur... 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.
Physical Review B, 2003
ABSTRACT The magnetic order resulting from an indirect exchange between magnetic moments provided... 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
Physical Review B, 1982
ABSTRACT The recent theory of Ferreira da Silva et al. for the specific heat of doped semiconduct... 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.
Physical Review B, 1981
ABSTRACT