Electron spin quantum beats and room temperature g factor in GaAsN

We report on the investigation of electron spin quantum beats at room temperature in GaAsN thin films by time-resolved Kerr rotation technique. The measurement of the quantum beats, which originate from the Larmor precession of electron spins in external transverse magnetic field, yields an accurate determination of the conduction electron g factor. We show that the g factor of GaAs1-xNx thin films is significantly changed by the introduction of a small nitrogen fraction.

Electric Field Control of Interface Related Spin Splitting in Step Quantum Wells

Spin splitting of the AlyGa1-yAs/GaAs/AlxGa1-xAs/AlyGa1-yAs (x not equal y) step quantum wells (QWs) has been theoretically investigated with a model that includes both the interface and the external electric field contribution. The overall spin splitting is mainly determined by the interface contribution, which can be well manipulated by the external electric field. In the absence of the electric field, the Rashba effect exists due to the internal structure inversion asymmetry (SIA). The electric field can strengthen or suppress the internal SIA, resulting in an increase or decrease of the spin splitting. The step QW, which results in large spin splitting, has advantages in applications to spintronic devices compared with symmetrical and asymmetrical QWs. Due to the special structure design, the spin splitting does not change with the external electric field.

Strong Spin-Orbit Interactions in an InAlAs/InGaAs/InAlAs Two-Dimensional Electron Gas by Weak Antilocalization Analysis

Spin-orbit interactions in a two-dimensional electron gas were studied in an InAlAs/InGaAs/InAlAs quantum well. Since weak anti localization effects take place far beyond the diffusive regime, (i.e., the ratio of the characteristic magnetic field, at which the magnetoresistance correction maximum occurs, to the transport magnetic field is more than ten) the experimental data are examined by the Golub theory, which is applicable to both diffusive regime and ballistic regime. Satisfactory fitting lines to the experimental data have been achieved using the Golub theory. In the strong spin-orbit interaction two-dimensional electron gas system, the large spin splitting energy of 6.08 meV is observed mainly due to the high electron concentration in the quantum well. The temperature dependence of the phase-breaking rate is qualitatively in agreement with the theoretical predictions. (C) 2009 The Japan Society of Applied Physics

Fine structural splitting and exciton spin relaxation in single InAs quantum dots

We have studied the exciton spin dynamics in single InAs quantum dots (QDs) with different exciton fine structural splitting (FSS) by transient luminescence measurements. We have established the correlation between exciton spin relaxation rate and the energy splitting of the FSS when FSS is nonzero and found that the spin relaxation rate in QD increases with a slope of 8.8x10(-4) ns(-1) mu eV(-1). Theoretical analyses based on the phonon-assisted relaxations via the deformation potential give a reasonable interpretation of the experimental results.

Spin-Hall effect in the generalized honeycomb lattice with Rashba spin-orbit interaction

We study the spin-Hall effect in a generalized honeycomb lattice, which is described by a tight-binding Hamiltonian including the Rashba spin-orbit coupling and inversion-symmetry breaking terms brought about by a uniaxial pressure. The calculated spin-Hall conductance displays a series of exact or approximate plateaus for isotropic or anisotropic hopping integral parameters, respectively. We show that these plateaus are a consequence of the various Fermi-surface topologies when tuning epsilon(F). For the isotropic case, a consistent two-band analysis, as well as a Berry-phase interpretation. are also given. (C) 2009 Elsevier B.V. All rights reserved.

Effect of Ka-band microwave on the spin dynamics of electrons in a GaAs/Al0.35Ga0.65As heterostructure

We report experimental results of the effect of Ka-band microwave on the spin dynamics of electrons in a two-dimensional electron system (2DES) in a GaAs/Al0.35Ga0.65As heterostructure via time-resolved Kerr rotation measurements. While the microwave reduces the transverse spin lifetime of electrons in the bulk GaAs, it significantly increases that in the 2DES, from 745 to 1213 ps, when its frequency is close to the Zeeman splitting of the electrons in the magnetic field. Such a microwave-enhanced spin lifetime is ascribed to the microwave-induced electron scattering which leads to a "motional narrowing" of spins via D'yakonov-Perel' mechanism.

Measuring spin diffusion of electrons in bulk n-GaAs using circularly dichromatic absorption difference spectroscopy of spin gratings

Circular dichromatic absorption difference spectroscopy is developed to measure the spin diffusion dynamics of electrons in bulk n-GaAs. This spectroscopy has higher detection sensitivity over homodyne detection of spin-grating-diffracted signal. A model to describe circular dichromatic absorption difference signal is derived and used to fit experimental signal to retrieve decaying rate of spin gratings. A spin diffusion constant of D-s=201 +/- 25 cm(2)/s for bulk n-GaAs has been measured at room temperature using this technique and is close to electron diffusion constant (D-c), which is much different from the case in GaAs quantum wells where D-s is markedly less than D-c.

Hole Spin Relaxation in an Ultrathin InAs Monolayer

We investigate the spin relaxation time of holes in an ultrathin neutral InAs monolayer (1.5 ML) and compare with that of electrons, using polarization-dependent time-resolved photoluminescence (TRPL) experiments. With excitation energies above the GaAs gap, we observe a rather slow relaxation of holes (tau(1h) = 196 +/- 17 ps) that is in the magnitude similar to electrons (tau(1e) = 354 +/- 32 ps) in this ultrathin sample. The results are in good agreement with earlier theoretical prediction, and the phonon scattering due to spin-orbit coupling is realized to play a dominant role in the carrier spin kinetics.

Quantum efficiency and temperature coefficients of GaInP/GaAs dual-junction solar cell

GaInP/GaAs dual-junction solar cell with a conversion efficiency of 25.2% has been fabricated using metalorganic chemical vapor deposition (MOCVD) technique. Quantum efficiencies of the solar cell were measured within a temperature range from 25 to 160A degrees C. The results indicate that the quantum efficiencies of the subcells increase slightly with the increasing temperature. And red-shift phenomena of absorption limit for all subcells are observed by increasing the cell's work temperature, which are consistent with the viewpoint of energy gap narrowing effect. The short-circuit current density temperature coefficients dJ (sc)/dT of GaInP subcell and GaAs subcell are determined to be 8.9 and 7.4 mu A/cm(2)/A degrees C from the quantum efficiency data, respectively. And the open-circuit cell voltage temperature coefficients dV (oc)/dT calculated based on a theoretical equation are -2.4 mV/A degrees C and -2.1 mV/A degrees C for GaInP subcell and GaAs subcell.

Spin relaxation and dephasing mechanism in (Ga,Mn)As studied by time-resolved Kerr rotation

Spin dynamics in (Ga,Mn)As films grown on GaAs(001) was investigated by Time-resolved magneto-optical Kerr effect. The Kerr signal decay time of (Ga,Mn)As without external magnetic field applied was found to be several hundreds picoseconds, which suggested that photogenerated polarized holes and magnetic ions are coupled as a ferromagnetic system. Nonmonotonic temperature dependence of relaxation and dephasing (R&D) time and Larmor frequency manifests that Bir-Aronov-Pikus mechanism dominates the spin R&D time at low temperature, while D'yakonov-Perel mechanism dominates the spin R&D time at high temperature, and the crossover between the two regimes is Curie temperature.

Entanglement evolution of a spin-chain bath coupled to a quantum spin

For an electron spin in coupling with an interacting spin chain via hyperfine-type interaction, we investigate the dynamical evolutions of the pairwise entanglement of the spin chain, and a correlation function joined the electron spin with a pair of chain spins in correspondence to the electron-spin coherence evolution. Both quantities manifest a periodic and a decaying evolution. The entanglement of the spin bath is significant in distinguishing the zero-coherence status exhibited in periodic and decoherence evolutions of the electron spin. The periodical concurrence evolution of the spin bath characterizes the whole system in a coherence-preserving phase, particularly for the case that the associated periodic coherence evolution is predominated by zero value in the infinite chain-length limit, which was often regarded as the realization of decoherence.

Quantum critical phenomena in the XY spin chain with the Dzyaloshinski-Moriya interaction (Retracted article. See vol 80, artn 019903, 2009)

We study the effects of the Dzyaloshinski-Moriya (DM) anisotropic interaction on the ground-state properties of the Heisenberg XY spin chain by means of the fidelity susceptibility, order parameter, and entanglement entropy. Our results show that the DM interaction could influence the distribution of the regions of quantum phase transitions and cause different critical regions in the XY spin model. Meanwhile, the DM interaction has effective influence on the degree of entanglement of the system and could be used to increase the entanglement of the spin system.

Structure, magnetization, and low-temperature spin dynamic behavior of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs

We have fabricated a set of samples of zincblende Mn-rich Mn(Ga)As clusters embedded in GaAs matrices by annealing (Ga,Mn)As films with different nominal Mn content at 650 degrees C. For the samples with Mn content no more than 4.5%, the Curie temperature reaches nearly 360 K. However, when Mn content is higher than 5.4%, the samples exhibit a spin-glass-like behavior. We suggest that these different magnetic properties are caused by the competing result of dipolar and Ruderman-Kittel-Kasuya-Yosida interaction among clusters. The low-temperature spin dynamic behavior, especially the relaxation effect, shows the extreme creeping effect which is reflected by the time constant tau of similar to 10(11) s at 10 K. We explain this phenomenon by the hierarchical model based on the mean-field approach. We also explain the memory effect by the relationship between the correlation function and the susceptibility.

Spin splitting of conduction subbands in Al0.3Ga0.7As/GaAs/AlxGa1-x As/Al0.3Ga0.7As step quantum wells

By means of the transfer matrix technique, interface-induced Rashba spin splitting of conduction subbands in Al0.3Ga0.7As/GaAs/AlxGa1-xAs/Al0.3Ga0.7As step quantum wells which contain internal structure inversion asymmetry introduced by the insertion of AlxGa1-xAs step potential is investigated theoretically in the absence of electric field and magnetic field. The dependence of spin splitting on the well width, step width and Al concentration is investigated in detail. We find that the sign of the first excited subband spin splitting changes with well width and step width, and is opposite to that of the ground subband under certain conditions. The sign and strength of the spin splitting are shown to be sensitive to the components of the envelope function at three interfaces. Copyright (C) EPLA, 2009

Anisotropic Spin Splitting in Step Quantum Wells

By the method of finite difference, the anisotropic spin splitting of the AlxGa1-xAs/GaAs/AlyGa1-yAs/AlxGa1-xAs step quantum wells (QWs) are theoretically investigated considering the interplay of the bulk inversion asymmetry and structure inversion asymmetry induced by step quantum well structure and external electric field. We demonstrate that the anisotropy of the total spin splitting can be controlled by the shape of the QWs and the external electric field. The interface related Rashba effect plays an important effect on the anisotropic spin splitting by influencing the magnitude of the spin splitting and the direction of electron spin. The Rashba spin splitting presents in the step quantum wells due to the interface related Rashba effect even without external electric field or magnetic field.