Aharonov-Bohm scattering by vortices of dimensionally-reduced Yang-Mills field

If two dimensions of six-dimensional space-time are compactified, a topological configuration of Yang-Mills gauge field appears as a cosmic string in four dimensions, whose thickness is of the same order as the size of the compact space. We consider scattering of low-energy fermions by this object.     

Transformation of optical vortices by polarization dynamic holograms

Results of theoretical and experimental studies of regularities in the transformation of the topological and polarization structures of optical vortices by polarization dynamic holograms formed by pulse Gaussian and singular light beams in dye solutions are presented.     

Optical restoration of photorefractive holograms

We consider the possibility of restoration and/or enhancement of decaying holograms in photorefractive media by using a simple optical readout in conjunction with a phase conjugator. The results indicate that extremely weak holograms can be enhanced provided that the two-beam coupling is sufficiently strong. Steady-state photorefractive holograms can be maintained continuously without decay by using a self-enhanced readout scheme. The results also provide an explanation for the formation of mutually pumped phase conjugation in terms of the amplification of an initial noise grating. The results are presented and discussed.     

Optical vortices in focal regions

Optical vortices in focal regions are studied using the Debye approximation. We discuss how scalar vortices give rise to different intensity structures in the focal region for a certain class of apertures. Vortices in cylindrical symmetric polarization distributions form new complex structures in the focal region, and in some cases the intensity is no longer zero on the optical axis. In particular, we find that for an azimuthal polarization distribution the local circulation deviates from that of the vortex impinging on the lens. On the other hand, upon using a radially polarized field distribution combined with an annular aperture, only the electric-field component along the optical axis remains, and the field structure is the same as in the scalar case.     

Repeated Compton scattering in a strong magnetic field

Science China Physics, Mechanics & Astronomy - Repeated scatterings of unpolarized photons by non-relativistic electrons in a static and uniform magnetic field are investigated by using the...     

Resonance Compton scattering in an external magnetic field

The scattering of a photon by an electron in an external magnetic field under resonant conditions, when the photon energy is close to the splittings between the Landau levels, is investigated. Formulas are obtained for the cross section of the process taking account of the polarization of the electron. For external fields ～10¹² G the resonant Compton cross section is several orders of magnitude greater than the Thompson cross section, and the width of the resonance is tens of electron volts.     

Pinning of planar vortices and magnetic field penetration in a three-dimensional Josephson medium

The behavior of planar (laminar) vortices in a three-dimensional, ordered Josephson medium as a function of the parameter I, which is proportional to the critical junction current and the cell size, is investigated with allowance for pinning due to the cellular structure of the medium. The minimum possible distances between two isolated vortices are calculated. A system of vortices formed in a sample in a monotonically increasing external magnetic field is analyzed. The minimum distance from the outermost vortex to the nearest neighbor is proportional to I ^−1.1. For I⩽1.3 each vortex contains a single flux quantum Φ₀, and the distance between them does not decrease in closer proximity to the boundary but remains approximately constant, implying that the magnetic field does not depend on the coordinate in the region penetrated by vortices. These facts contradict the generally accepted Bean model. The sample magnetization curve has a form typical of type II superconductors. Allowance for pinning raises the critical field H _c and induces a sudden jump in the curve at H=H _c. Zh. Tekh. Fiz. 67, 38–46 (September 1997)     

The scattering of electrons moving in a magnetic field

The problem investigated here is that of the scattering of relativistic electrons by a spherically symmetric force center. In contrast to the usual formulation of the problem it is assumed that the electrons are traveling in a constant and uniform magnetic field.     

Dynamics of magnetic vortices

The canonical conservation laws of linear and angular momentum in the ferromagnetic continuum have been known to be plagued by certain ambiguities which are resolved in this paper by constructing conservation laws as suitable moments of a topological density. The resulting canonical structure is then shown to be analogous to that encountered in the familiar Hall effect and explains the unusual features of the dynamics of magnetic vortices without resorting to a detailed solution of the underlying nonlinear equations. Thus, in the absence of external magnetic fields, a magnetic vortex is shown to be spontaneously pinned around a fixed guiding center. The guiding center would drift in a direction perpendicular to an applied magnetic field gradient, provided that dissipation can be neglected, with a Hall velocity that is calculated explicitly in terms of the initial configuration of the vortex. In the presence of dissipation, the vortex undergoes skew deflection at an angle δ ≠ 90° with respect to the applied field gradient. The angle δ is related to the winding number of the vortex according to the well-known golden rule of bubble dynamics.     

Drift of domain walls in a harmonic magnetic field

It is shown that a two-step form of the dynamic magnetization curve (and the hysteresis loop) established for a multiaxial ferrite-garnet wafer with a low quality factor (Q < 1) and considerable anisotropy in the plane (K _p /K _u = 14) in the frequency range of 25–1000 Hz is explained by the reconstruction of the dynamic domain structure, particularly by the established features of the drift of domain boundaries in the harmonic magnetic field.     

Optical phonons of Rare-Earth halides in a magnetic field

A theory is developed which explains the observed magnetic field splitting of doubly degenerateE-phonons in Rare Earth Chlorides. It is based on first and second order magnetoelastic interactions. Quantitative calculations are done for CeCl₃ for which the field dependence of the splitting is derived and estimates of the coupling constants are given.Furthermore we propose a mechanism for the observed reduction of the phononlinewidth in a magnetic field.     

Velocity field vortices and Mermin-Ho vortices in two-component spinor BEC

In light of the φ-mapping topological current theory, two important vortex structures in two-component spinor BEC—the velocity field vortices and the Mermin-Ho vortices are discussed. It is revealed that these two different kinds of vortices are created respectively from the zero points of two different order parameter configurations in the condensates, and both their topological charges, locations and motions can be determined by the φ-mapping theory.     

Magnetic domain wall dynamics in an inhomogeneous magnetic field

A new experimental method for the study of single magnetic domain wall dynamics in bistable microwires is presented. It raises new possibilities for experimenting with a single magnetic domain wall moving in an inhomogeneous magnetic field. Models for a wall with fixed length were confronted with experimental data obtained on amorphous glass-coated ferromagnetic Fe_77.5B₁₅Si_7.5${\mathrm{Fe}}_{77.5}{\mathrm{B}}_{15}{\mathrm{Si}}_{7.5}$ microwire. These models qualitatively describe the observed behavior. The accord between models and experiment increases as the field disturbance decreases due to its inhomogeneity. A better match between experimental and model curves can probably be obtained if the changes in the wall dimensions and wall mass are taken into account.     

Linear magnetoresistance and magnetic field dependent scattering probability

Within the framework of the Boltzmann equation it is possible to find a linear behaviour for the Magnetoresistance. Instead of using a purely random impurity scattering model, one makes this model slightly magnetic field dependent. Keeping only the linear term of the power expansion in the magnetic field, one finds a linear dependence of the Magnetoresistance.     

Manipulating vortices in F=2 Bose-Einstein condensates through magnetic field and spin-orbit coupling

We investigate the vortex structures excited by Ioffe-Pritchard magnetic field and Dresselhaus-type spin-orbit coupling in F=2 ferromagnetic Bose-Einstein condensates. In the weakly interatomic interacting regime, an external magnetic field can generate a polar-core vortex in which the canonical particle current is zero. With the combined effect of spin-orbit coupling and magnetic field, the ground state experiences a transition from polar-core vortex to Mermin-Ho vortex, in which the canonical particle current is anticlockwise. For fixed spin-orbit coupling strengths, the evolution of phase winding, magnetization, and degree of phase separation with magnetic field are studied. Additionally, with further increasing spin-orbit coupling strength, the condensate exhibits symmetrical density domains separated by radial vortex arrays. Our work paves the way to explore exotic topological excitations in high-spin systems.