International Journal of Modern Physics B

We review Floquet formalism of quantum electron pumps. In the Floquet formalism the quantum pump is regarded as a time dependent scattering system, which allows us to go beyond the adiabatic limit. It can be shown that the well-known adiabatic formula given by Brouwer can be derived from the adiabatic limit of Floquet formalism. We compare various physical properties of the quantum pump both in the adiabatic and in the non-adiabatic regime using the Floquet theory.

Modeling statistical properties of motion of a Lagrangian particle advected by a high-Reynolds-number flow is of much practical interest and complement traditional studies of turbulence made in Eulerian framework. The strong and nonlocal character of Lagrangian particle coupling due to pressure effects makes the main obstacle to derive turbulence statistics from the three-dimensional Navier–Stokes equation; motion of a single fluid-particle is strongly correlated to that of the other particles. Recent breakthrough Lagrangian experiments with high resolution of Kolmogorov scale have motivated growing interest to acceleration of a fluid particle. Experimental stationary statistics of Lagrangian acceleration conditioned on Lagrangian velocity reveals essential dependence of the acceleration variance upon the velocity. This is confirmed by direct numerical simulations. Lagrangian intermittency is considerably stronger than the Eulerian one. Statistics of Lagrangian acceleration depends on Reynolds number. In this review we present description of new simple models of Lagrangian acceleration that enable data analysis and some advance in phenomenological study of the Lagrangian single-particle dynamics. Simple Lagrangian stochastic modeling by Langevin-type dynamical equations is one the widely used tools. The models are aimed particularly to describe the observed highly non-Gaussian conditional and unconditional acceleration distributions. Stochastic one-dimensional toy models capture main features of the observed stationary statistics of acceleration. We review various models and focus in a more detail on the model which has some deductive support from the Navier–Stokes equation. Comparative analysis on the basis of the experimental data and direct numerical simulations is made.

A quick and relatively simple technique for stripping off Si wafers of its native oxide and carbon impurities, using pulsed laser ablation at room temperature, is presented. In a chamber at 10^-10 Torr, an oxidized Si(100) surface is ablated with 248 nm UV radiation from a KrF excimer laser. Experiments using 200 pulses of different laser energy densities were performed until a clean surface, at 600 mJ/cm², was obtained as determined by Auger electron spectroscopy and ellipsometry measurements. The slightly out of focus laser beam is scanned over the selected area leaving an atomically 1×1 feceted Si surface, as shown by RHEED. The familiar 1×2 reconstructed Si surface may be obtained through a post annealing process.

This article deals with the connection between diagonal matrix elements <r^k> for 3H- and DH-atoms and the property of Appell's function F₂(1, 1) mirror-like symmetry with respect to the center j₀=-1/2 under the substitution j↦-j-1, j∈ℤ. Exact numerical values for <r^k>_nl of a 3H-atom, as n≤8 and -7≤k≤4, in the form of regular rational fractions are first given, i.e. practically for all the D. I. Mendeleev table.

The lattice structure and electronic properties of perfect and defective CoSi₂ and NiSi₂ have been calculated using an ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximations (GGA). Special attention is paid to the formation energies of the vacancies, which largely depend on the atomic chemical potentials of Si and metal atom: in Si-rich limit, the formation energies of Si and Co vacancies are 2.39 eV and 0.56 eV whilst those are 1.53 eV and 2.29 eV in Co-rich limit in CoSi₂, respectively. For NiSi₂, the formation energies of Si and Ni vacancies are 0.56 eV and 1.25 eV in Si-rich limit and those are 0.04 eV and 2.3 eV in Ni-rich limit.

We use the effective mass model to describe spinless electrons near the Fermi level in metallic, single-wall carbon nanotubes. Taking into account two nonequivalent valleys (K-points) produces a four component Dirac equation for massless fermions, with the role of spin assumed by pseudospin due to the relative amplitude of the wavefunction on the two nonequivalent sublattice atoms. We show that the position of a short-ranged impurity within the hexagonal graphite unit cell produces a particular 4×4 matrix structure of the corresponding effective Hamiltonian. The symmetry of this Hamiltonian with respect to pseudospin flip is related to degeneracy breaking and, for an armchair tube, symmetry with respect to mirror reflection in the nanotube axis is related to pseudospin mixing. In a nanotube of finite length, we predict a sinusoidal oscillation of energy level shift as a function of energy with a period determined by the position of the impurity along the tube axis.

We study the energetic stability of the self-trapped magnetic polaron in an antiferromagnetic lattice of localized spins, including the effects of the intra-sublattice hopping which allows electron transfer within the same magnetic sublattice. The model consists of an itinerant electron moving in a one-dimensional antiferromagnetic lattice of localized spins. In addition to the first and the second neighbor electron hopping, terms describing the superexchange between the localized spins as well as the Hund's-rule coupling between the electron and the localized spins are included in the model Hamiltonian. The ground-state energy of the self-trapped polaron with the resulting ferromagnetic core region is compared with the energy of the propagating state in the antiferromagnetic lattice. We find the magnetic polaron to be self-trapped for all values of the Hamiltonian parameters, although the intra-sublattice hopping substantially reduces the polaron binding energy.

The concept of magnetic polaron is analyzed and developed to elucidate the nature of itinerant charge carrier states in magnetic semiconductors and similar complex magnetic materials. By contrasting the scattering and bound states of carriers within the s–d exchange model, the nature of bound states at finite temperatures is clarified. The free magnetic polaron at certain conditions is realized as a bound state of the carrier (electron or hole) with the spin wave. Quite generally, a self-consistent theory of a magnetic polaron is formulated within a nonperturbative many-body approach, the Irreducible Green Functions (IGF) method which is used to describe the quasiparticle many-body dynamics at finite temperatures. Within the above many-body approach we elaborate a self-consistent picture of dynamic behavior of two interacting subsystems, the localized spins and the itinerant charge carriers. In particular, we show that the relevant generalized mean fields emerges naturally within our formalism. At the same time, the correct separation of elastic scattering corrections permits one to consider the damping effects (inelastic scattering corrections) in the unified and coherent fashion. The damping of magnetic polaron state, which is quite different from the damping of the scattering states, finds a natural interpretation within the present self-consistent scheme.