International Journal of Modern Physics B

It is shown that in a single-axis antiferromagnetic semiconductor placed in a strong magnetic field, dispersionless magnons start emitting at any arbitrarily small velocity of an electron occurring in a spinpolaron state. If magnons are dispersed they are generated when the spinpolaron velocity exceeds the minimum phase velocity of magnons. The maximum power of magnon generation caused by the drift of spinpolarons is estimated.

The Zn-doped YBCO single crystals were prepared with Zn contents of 0.5%, 1.5%, 2.5%, 3.0% and 4.3%. The magnetic measurements were made under magnetic field up to 5 T using SQUID. The peak effect was observed in these samples in all the measured temperature range from 0.2 ≤ T/T_c ≤ 0.95. The region between peak field H_p and irreversibility field H_irr increased consistently with increasing Zn concentration showing broadening in the phase diagram and indicating increased disorder for higher Zn content samples. The anisotropy in the peak field H_p for these samples measured for applied field H along c-axis and along ab-plane (H_p‖c/H_p‖ab) was found to increase from 0.15 to 0.18 for samples with Zn concentration up to 3% and decreased to 0.142 for sample with Zn content of 4.3% at 0.9 T_c. In the temperature range of 0.8–0.95 T_c, the anisotropy in the critical current density (J_c|c/J_c‖ab) was also found to increase in the order of 1.9–2.166 for the samples with Zn content up to 3%, whereas for 4.3% Zn sample it was 0.926. The anisotropic changes in the irreversibility field H_irr were also found to be in the range of 0.254–0.279 for the Zn concentration up to 3% and decreased for the 4.3% Zn sample in temp range of 0.8–0.95 T_c. In addition to the effect of local magnetic moments induced by Zn impurity, the changes in the anisotropic factor with the increase of Zn content seems to contribute effectively for increase in H_p, J_c and H_irr for Zn contents up to 3% samples even at elevated temperature of 0.8–0.95 T_c. The decrease in J_c and H_irr for 4.3% Zn sample may be due to increase in the impurity level beyond threshold leading to decrease in superconducting volume fraction.

Exact analytical expressions for the Dirac–Slater–Marvin radial integrals of the type , and by means of Gauss's functions ₂F₁(z) and also their exact numerical values are first given. (Author has all the values of these integrals for arbitrary nlj-states of H-like for Z≤137, i.e., actually for all Mendeleev's table.)

The electronic structure and magnetism of CrSb compounds have been studied by a periodic quantum-mechanical calculation based on density functional theory. The results show that a ferrimagnetic ordered phase of CrSb in the Zinc-blende structure (ZB) is stable with half metallic properties, whereas the antiferromagnetic phase of CrSb in the NiAs-type crystal structure is energetically favored with no-gap band. The lattice constants have significant influence on the magnetism of CrSb. The band gap and the magnetic moment of Cr atom increase with increasing lattice constant in ZB CrSb. The effects on magnetic moment in the NiAs-type crystal structure are more sensitive substantially to the change of lattice constant a as compared with that of the lattice constant c. It is found that apart from ionic or metallic bonds there are covalent bonds between Crd and Sb p orbitals in ZB CrSb, while bonding between Cr and Sb atoms is mainly ionic or metallic in CrSb of NiAs structure.

We study the trading activity in the Korea Stock Exchange by considering trade avalanches. A series of successive trading with small trade time interval is regarded as a trade avalanche of which the size s is defined as the number of trade in a series of successive trades. We measure the distribution of trade avalanches sizes P(s) and find that it follows the power-law behavior P(s) ~ s^-α with the exponent α ≈ 2 for two stocks with the largest number of trades. A simple stochastic model which describes the power-law behavior of the distribution of trade avalanche size is introduced. In the model it is assumed that the some trades induce the accompanying trades, which results in the trade avalanches and we find that the distribution of the trade avalanche size also follows power-law behavior with the exponent α ≈ 2.

An exact map for Sinai's billiard with maximal central scatterer has been deduced from geometrical principles. Using this map a simple numerical method has been implemented for the search of periodic orbits. Results that seem to be useful in classical as quantum chaos are shown.

We study the transport properties of classical particles in the ballistic regime trapped in a two-dimensional channel with dephased ripple boundaries. By taking into account small ripple amplitudes, an analytical approximate expression for the classical resistivity is obtained. We show that the resistivity can be increased considerably by dephasing the walls of the channel. Our results are compared with those obtained for a channel composed of flat and sinusoidal boundaries.

Based on nonequilibrium Green's function and first-principles calculations, we investigate the electronic transport properties of 4,4′-biphenyldithiol functionalized molecular junction with different torsion angles between two phenyl rings. Numerical results show that torsion angle plays an important role in the conducting behavior of molecular junction. By changing the torsion angle, molecule can exhibit a switching behavior. Especially, when the molecule is functionalized with NO₂ side group, it will perform a molecular memory effect. Furthermore, effects of different adsorption positions of sulfur atom on molecular memory are also discussed.

This paper presents a novel unified hyperchaotic system that contains the hyperchaotic Lorenz system and the hyperchaotic Chen system as two dual systems at the two extremes of its parameter spectrum. The new system is hyperchaotic over almost the whole range of the system parameter and continuously transfers from the hyperchaotic Lorenz system to the hyperchaotic Chen system. The new findings are not only demonstrated by computer simulations but also verified with bifurcation analysis, Lyapunov exponents and Lyapunov dimension.

A non-isospectral and variable-coefficient modified Korteweg–de Vries (mKdV) equation is investigated in this paper. Starting from the Ablowitz–Kaup–Newell–Segur procedure, the Lax pair is established and the Bäcklund transformation in original variables is also derived. By a dependent variable transformation, the non-isospectral and variable-coefficient mKdV equation is transformed into bilinear equations, by virtue of which the N-soliton-like solution is obtained. In addition, the bilinear Bäcklund transformation gives a one-soliton-like solution from a vacuum one. Furthermore, the N-soliton-like solution in the Wronskian form is constructed and verified via the Wronskian technique.

We use cluster generalization of the coherent potential approximation in the tight-binding linear muffin-tin orbital method to account for the effect of the local environment on electronic and magnetic properties of substitutional random alloys. This theory combines the augmented space formalism and conventional tight-binding linear muffin-tin orbital methods. In particular, we shall apply the technique to the bcc-based NiAl and fcc-based CuAu alloys and also compare with other approaches.