The effects of Dresselhaus and Rashba spin-orbit interactions on the electron tunneling in a non-magnetic heterostructure

We theoretically investigate the electron transport properties in a non-magnetic heterostructure with both Dresselhaus and Rashba spin-orbit interactions. The detailed-numerical results show that (1) the large spin polarization can be achieved due to Dresselhaus and Rashba spin-orbit couplings induced splitting of the resonant level, although the magnetic field is zero in such a structure, (2) the Rashba spin-orbit coupling plays a greater role on the spin polarization than the Dresselhaus spin-orbit interaction does, and (3) the transmission probability and the spin polarization both periodically change with the increase of the well width.     

Transport of waves in disordered waveguides: A potential model

We study the statistical properties of wave transport in a disordered waveguide. We first derive the properties of a “building block” (BB) of length δL starting from a potential model consisting of thin potential slices. We then find a diffusion equation—in the space of transfer matrices that describe our system—which governs the evolution with the length L of the disordered waveguide of the transport properties of interest. The latter depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. We have developed a numerical simulation in which the universal statistical properties of the BB found analytically are first implemented numerically, and then the various BBs are combined to construct the full waveguide. The reported results thus obtained are in good agreement with microscopic calculations, for both bulk and surface disorder.     

Observation of internal-conversion electrons induced by inelastic nuclear resonant scattering

Measurements of the internal-conversion electron emission due to the inelastic nuclear resonant excitation are reported. thin films of 20 and 1.3 nm thickness were deposited on Si(1 1 1), and the internal-conversion electrons were measured as a function of the photon energy. From the inelastic part of the spectra, the phonon density of states was obtained. Whereas the phonon density of states of 20-nm thick film resembles that of bulk -Fe, the 1.3-nm thick film revealed an obvious softening of the acoustic mode.     

The bias- and temperature-dependent electron transport in a magnetic nanostructure

In this paper, we theoretically investigate the effect of the bias and temperature on the electron transport properties in a magnetic nanostructure. It is found that the large spin-polarization can be achieved in such a nanostructure, and the degree of spin-polarization obviously increases with increasing applied bias. It is also found that the conductance curves for the different temperatures obviously intersect at the same Fermi energy for the low Fermi energy, and the degree of spin-polarization decreases with the increase of temperature. Thus, we can control the electron transport through changing the bias and temperature.     

Anomalies of the phonon properties in multiferroic BiFeO3 thin films near the magnetic phase transition temperature

Size, substrate, doping and magnetic field effects on the phonon properties in multiferroic BiFeO₃ thin films are studied based on a microscopic model. We obtain an anomaly near the magnetic phase transition temperature TN which can be attributed to the magnetoelectric nature of BiFeO₃ and strong anharmonic spin-phonon interaction. It is shown that due to crystal lattice distortion for dopants with ionic radius smaller than that of the host ions the phonon energy decreases (for example Tb or Ti), whereas for the opposite case (larger radius of the doping ions, for example Co or Ni) it increases. The phonon damping is always enhanced compared to the undoped thin film.     

Magnetic ground state and spin waves in A(A = K, Rb or Cs)Fe1.5Se2

We present theoretical results on the ground state phase diagram, spin waves and dynamic structure factor on the J₁-J₂ model. In the reasonable physical parameter region corresponding to AFe_1.5Se₂, the A-collinear antiferromagnetic phase is stable. The spin wave spectra have two acoustic branches and four optical branches for this phase on the rhombus-ordered vacancy lattice, and each of them is twofold degenerate. However, they have one nondegenerate acoustic branch and two nondegenerate optical branches on the square-ordered vacancy lattice. To offer the theoretical guidance for the further experiments, we also discuss the magnetic excitation spectra and the inelastic neutron scattering pattern based on linear spin wave theory.     

Grouping and adding method for calculating light scattering by large fluffy aggregates

We present a method to derive the light scattering properties of very porous fractal aggregates composed of a large number of monomers where the size parameter of monomer is larger than unity. Our new method is based on the grouping of the aggregate: The aggregate is divided into groups, where each group is located along a line of the incident light, and the scattering properties of the group are calculated taking into account multiple scattering with monomers located inside the group, as well as those in a buffer region around the group. The scattering and absorption efficiencies are obtained by adding the resultant scattering properties for all the groups. We have shown that the method effectively works when the monomer scatters the incident lights predominantly in the forward direction, which is the case if the monomer size is large compared to the wavelength of the incident light.The errors in resulting scattering and absorption efficiencies for porous aggregates are investigated for various refractive indices and sizes of monomers. We found that the errors are larger for low absorbing materials and they can be reduced by expanding the buffer region. In the case of the buffer region for each group consisting of 1/8 of the total number of monomers, the results show errors less than 15% and 10% for absorption and scattering, respectively. It is also shown that the errors have a small standard deviation (i.e., 2%) for different directions of the incident light.     

Nanostructural and surface morphological evolution of chemically sprayed SnO2 thin films

Physical properties of a nanocrystalline thin film is greatly influenced by its morphological and structural evolution. We try to understand the transition of SnO₂ thin films from amorphous to nanocrystalline structure with XRD, IR, SEM, AFM and surface profiler studies. A 2D layer like structure resulting from quantum confinement is found for the films prepared at 400 °C. We observed a new IR band at 530 cm⁻¹ that was theoretically predicted and report it for the first time. A correlation of population of defects in SnO₂ films with change in lattice parameters and FWHM of IR bands are reported. The electric and optical properties of the films have been discussed.     

Ultrafast laser-driven magnetic-switching scenario in NiO: Role of phonons

We present a fully ab initio ultrafast magnetooptical-switching mechanism in NiO. After obtaining all intragap d-character states of the bulk and the (001) surface with the use of highly correlational quantum chemistry we propagate in time under the influence of a static magnetic field and a laser pulse. We find that switching can be best achieved in a subpicosecond regime with linearly polarized light. The electric-dipole approximation suffices for the surface, however, for the centrosymmetric bulk the presence of an optical phonon is used as a symmetry-lowering mechanism. Lattice (contrary to electronic) temperature is found to enhance the process.     

Cusps in KL→3π decays

The pronounced cusp in K→3π decays which is generated by the pion mass difference is directly related to the ππS-wave scattering lengths. We apply a nonrelativistic effective field theory framework to evaluate the amplitudes for K_L→3π decays in a systematic manner. Electromagnetic effects in the neutral channel K_L→3π⁰ are also discussed.     

Magnetic properties of a ferrimagnetic core/shell nanocube Ising model: A Monte Carlo simulation study

Monte Carlo simulation has been used to study the magnetic properties and hysteresis loops of a single nanocube, consisting of a ferromagnetic core of spin- surrounded by a ferromagnetic shell of spin-1 with antiferromagnetic interface coupling. We find a number of characteristic phenomena. In particular, the effects of the shell coupling and the interface coupling on both the compensation temperature and the magnetization profiles are investigated. The effects of the interface coupling on the hysteresis loops are also examined.     

Phonon spectra of a Fibonacci chain

Based on more realistic physics we study the phonon spectra of the Fibonacci chain by taking into account a nonlinear resistance. It is found that the nonlinear force should be very weak and consequently, the continuity, range and gaps of the phonon spectra would be still controlled dominantly by the relative strength of spring constants and chain length. It means that even if no additional nonlinear resistance was taken into account, the conventional results of phonon spectra are exactly correct. On the other hand, in the framework of a conventional model we investigated the relationship between the biggest gaps of phonon spectra and defects of Fibonacci-like aperiodic chains. By means of numerical calculations one can obtain quantitatively the maximum of the length of a one-dimensional aperiodic chain sensitive to boundaries. This method would be useful for the calculation of quasiperiodic and aperiodic lattices.     

Multifractal detrended fluctuation analysis of derivative and spot markets

We investigate the multifractal properties of price increments in the cases of derivative and spot markets. Through the multifractal detrended fluctuation analysis, we estimate the generalized Hurst and the Renyi exponents for price fluctuations. By deriving the singularity spectrum from the above exponents, we quantify the multifractality of a financial time series and compare the multifractal properties of two different markets. The different behavior of each agent-group in transactions is also discussed. In order to identify the nature of the underlying multifractality, we apply the method of surrogate data to both sets of financial data. It is shown that multifractality due to a fat-tailed distribution is significant.     

Influence of surface heterogeneity in electroosmotic flows—Implications in chromatography, fluid mixing, and chemical reactions in microdevices

We analyze the influence of surface heterogeneity, inducing a random ζ-potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ-potential heterogeneity, spatial randomness in the surface ζ-potential modifies the spectral properties of the advection-diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.     

The static and dynamic properties of PuCoGa5 and NpCoGa5 investigated by neutron scattering experiments

Neutron scattering results on single crystals shed light on the static and dynamic properties of the superconductor () PuCoGa₅ and its isostructural but antiferromagnetic () homologue NpCoGa₅. By polarized neutron diffraction the magnetization density in the paramagnetic state of both compounds has been inferred. The microscopic magnetization of NpCoGa₅ is consistent with the orbital and spin components of a localized Np³⁺ magnetic moment. In the case of PuCoGa₅ the microscopic magnetization is small, temperature-independent and cannot be described as a localized Pu³⁺ magnetic moment. For NpCoGa₅ a dynamic magnetic signal has been observed by three-axis spectroscopy in the antiferromagnetically ordered state. The magnetic signal is strongest at the antiferromagnetic zone center and an energy transfer of about 5 meV. Magnetic fluctuations persist at this position in the paramagnetic state. The dynamic response is similar to the dynamic response observed in other actinide intermetallic compounds. This supports the possibility that magnetic fluctuations could also be present in the paramagnetic superconductor PuCoGa₅.     

Quaternary metallic ferrimagnets based on antiferromagnetic semiconductor MnTe

We use an accurate full-potential density-functional method to systematically study MnTe-based quaternary magnetic compounds: Mn₆ZnAlTe₈, Mn₆ZnGaTe₈, Mn₆CdAlTe₈, and Mn₆CdGaTe₈. The co-substitution of group-II and group-III atoms for a quarter of Mn atoms changes the antiferromagnetic MnTe semiconductor into ferrimagnetic (FM) metal because the extra electron, introduced by the trivalent atom, as effective carrier makes Mn spins within nonmagnetic substitutional layers orient uniformly. Quite high spin polarization can be achieved for the electrons at the Fermi level in the co-substituted structures. This could make a novel approach to promising FM materials. The quaternary metallic ferrimagnets could have potential applications for spintronic devices.     

Frequency-dependent linear and non-linear response properties of single carrier quantum dots: Role of effective mass and anharmonicity in the confinement potential

We explore the pattern of frequency-dependent linear and non-linear optical (NLO) response of one electron quantum dots harmonically confined in two dimensions. For some fixed values of transverse magnetic field strength (ω_c), and harmonic confinement potential (ω₀), the influence of effective mass (m^*) of the system and the symmetry breaking anharmonic interaction on the frequency-dependent linear (α), and the first (β), and second (γ) NLO responses of the dot is computed through linear variational route. The investigation reveals interesting roles played by the anharmonic interaction and effective mass in modulating the response properties.     

Metallic nanosieves formed by ultra-short-pulse laser ablation

The formation of free-standing gold nanosieves by ablation with ultra-short laser pulses is demonstrated. Macroscopic areas are generated fast and efficiently by the application of a parallel production technique. The technique is based on a lens array formed by self-assembling quartz microspheres on a thin metal foil. The evaporated foils have a final thickness of 400 nm, and the hole spacing is set by the diameter of the microspheres (∼7 m) while the pore size is ∼700 nm. The characteristic spacing of the generated hole structure is verified by an optical diffraction technique.     

Aluminium adsorption on Ir(1 1 1) at a quarter monolayer coverage: A first-principles study

We present an ab initio density-functional study for aluminium adsorption on Ir(1 1 1) at high symmetry sites, namely, the fcc-, hcp-hollow, top and bridge sites. In each case, we calculate the atomic geometry, average binding energy, work function, and surface dipole moment at the coverage of 0.25 monolayer. We find the favourable structure to be Al at threefold hcp-hollow site, with a corresponding binding energy of 4.46 eV. We present and compare the electronic properties of the two lowest energy structures, i.e., at the threefold hollow sites and discuss the nature of the Al-Ir bond and binding site preference. In particular, we observe a large hybridization of Al-3s, 3p and Ir-5d states near Fermi level, forming an inter-metallic bonds. This results in a significant electron transfer from the Al atoms to the Ir(1 1 1) substrate, inducing an outward pointing surface dipole moment and a large decrease in the work function of 1.69 eV for Al in the hcp-hollow site. Compared to the fcc-hollow site, adsorption in the hcp-hollow site results in a lower density-of-states at the Fermi level, as well as a greater hybridization in the bonding states.