10 research outputs found
Ultrafast spin dynamics in II-VI diluted magnetic semiconductors with spin-orbit interaction
We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic
semiconductors in the presence of spin-orbit interaction. Our goal is to
explore the interplay or competition between the exchange -coupling and the
spin-orbit interaction in both bulk and quantum well systems. For bulk
materials we concentrate on ZnMnSe and take into account the
Dresselhaus interaction, while for quantum wells we examine
HgMnCdTe systems with a strong Rashba coupling. Our
calculations were performed with a recently developed formalism which
incorporates electronic correlations beyond mean-field theory originated from
the exchange -coupling. For both bulk and quasi-two-dimensional systems we
find that, by varying the system parameters within realistic ranges, both
interactions can be chosen to play a dominant role or to compete on an equal
footing with each other. The most notable effect of the spin-orbit interaction
in both types of systems is the appearance of strong oscillations where the
exchange -coupling by itself only causes an exponential decay of the mean
electronic spin components. The mean-field approximation is also studied and it
is interpreted analytically why it shows a strong suppression of the
spin-orbit-induced dephasing of the spin component parallel to the Mn magnetic
field.Comment: 9 pages, 5 figure
Quantum correlations of a two-dimensional electron gas with Rashba spin-orbit coupling
We study the correlations of a two-dimensional electron gas with Rashba spin-orbit coupling (SOC). We obtain the two-particle density matrix and use it to derive the exchange hole. We find a nontrivial correlation for electrons with opposite spin projections that does not occur without Rashba SOC. The two-particle density matrix allows us to further study the quantum correlations of the system. We use it to obtain the concurrence and the entanglement of formation in order to quantify the entanglement of the electron spins. Additionally, we calculate the quantum discord and compare it with the entanglement and classical correlations.Fil: Aranzadi, J. I.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FÃsica; ArgentinaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; Argentin
Spin-orbit effects in nanowire-based wurtzite semiconductor quantum dots
We study the effect of the Dresselhaus spin-orbit interaction on the
electronic states and spin relaxation rates of cylindrical quantum dots defined
on quantum wires having wurtzite lattice structure. The linear and cubic
contributions of the bulk Dresselhaus spin-orbit coupling are taken into
account, along with the influence of a weak external magnetic field. The
previously found analytic solution for the electronic states of cylindrical
quantum dots with zincblende lattice structures with Rashba interaction is
extended to the case of quantum dots with wurtzite lattices. For the electronic
states in InAs dots, we determine the spin texture and the effective g-factor,
which shows a scaling collapse when plotted as a function of an effective
renormalized dot-size dependent spin-orbit coupling strength. The
acoustic-phonon-induced spin relaxation rate is calculated and the transverse
piezoelectric potential is shown to be the dominant one.Comment: 12 pages, 5 figure
Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling
We identify the Dresselhaus spin-orbit coupling as the source of the dominant
spin-relaxation mechanism in the impurity band of doped semiconductors. The
Dresselhaus-type (i.e. allowed by bulk-inversion asymmetry) hopping terms are
derived and incorporated into a tight-binding model of impurity sites, and they
are shown to unexpectedly dominate the spin relaxation, leading to
spin-relaxation times in good agreement with experimental values. This
conclusion is drawn from two complementary approaches employed to extract the
spin-relaxation time from the effective Hamiltonian: an analytical
diffusive-evolution calculation and a numerical finite-size scaling.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Relaxation mechanism for electron spin in the impurity band of n-doped semiconductors
We propose a mechanism to describe spin relaxation in n-doped III-V
semiconductors close to the Mott metal-insulator transition. Taking into
account the spin-orbit interaction induced spin admixture in the hydrogenic
donor states, we build a tight-binding model for the spin-dependent impurity
band. Since the hopping amplitudes with spin flip are considerably smaller than
the spin conserving counterparts, the resulting spin lifetime is very large. We
estimate the spin lifetime from the diffusive accumulation of spin rotations
associated with the electron hopping. Our result is larger but of the same
order of magnitude than the experimental value. Therefore the proposed
mechanism has to be included when describing spin relaxation in the impurity
band.Comment: 4 page
Spin-relaxation time in the impurity band of wurtzite semiconductors
International audienceThe spin-relaxation time for electrons in the impurity band of semiconductors with wurtzite crystal structure is determined. The effective Dresselhaus spin-orbit interaction Hamiltonian is taken as the source of the spin relaxation at low temperature and for doping densities corresponding to the metallic side of the metal-insulator transition. The spin-flip hopping matrix elements between impurity states are calculated and used to set up a tight-binding Hamiltonian that incorporates the symmetries of wurtzite semiconductors. The spin-relaxation time is obtained from a semiclassical model of spin diffusion, as well as from a microscopic self-consistent diagrammatic theory of spin and charge diffusion in doped semiconductors. Estimates are provided for particularly important materials. The theoretical spin-relaxation times compare favorably with the corresponding low-temperature measurements in GaN and ZnO. For InN and AlN, we predict that tuning of the spin-orbit coupling constant induced by an external potential leads to a potentially dramatic increase of the spin-relaxation time related to the mechanism under study