Dynamics of vortex dipoles in confined Bose-Einstein condensates

We present a systematic theoretical analysis of the motion of a pair of straight counter-rotating vortex lines within a trapped Bose-Einstein condensate. We introduce the dynamical equations of motion, identify the associated conserved quantities, and illustrate the integrability of the ensuing dynamics. The system possesses a stationary equilibrium as a special case in a class of exact solutions that consist of rotating guiding-center equilibria about which the vortex lines execute periodic motion; thus, the generic two-vortex motion can be classified as quasi-periodic. We conclude with an analysis of the linear and nonlinear stability of these stationary and rotating equilibria.     

Branching optical signals by fractional vortex dipoles

We study the evolution and interaction of semi-infinite dark beams carrying phase dislocations, where step- and screw-like phase profiles are combined. Similar to dark beams with a finite length, semi-infinite dark beams tend to move in transversal direction with respect to their background beam. In addition, they develop a snake-like instability and optical vortices detach from their bending ends. We are looking for appropriate conditions to control the process of concatenating and crossing the ends of several such semi-infinite dark beams in a way suitable for probe-beam branching and routing in self-defocusing Kerr nonlinear media. Colinear and perpendicular probe beam propagations in the optically-induced guiding structures are modeled and analyzed with respect to the branching efficiency to respective virtual output channels.     

Magnus force and magnetic vortex dynamics in weak ferromagnets

The problem of steady motion of the magnetic vortex in a moving domain wall under the action of the Magnus force in weak ferromagnets was studied. Dynamic bending of the domain wall containing a moving vortex was analyzed. The formulas describing the dependences of the vortex velocity on the velocity of the domain wall in which it moves were derived.     

Scattering of vortex pairs in 2D easy-plane ferromagnets

Vortex-antivortex pairs in 2D easy-plane ferromagnets have characteristics of solitons in two dimensions. We investigate numerically and analytically the dynamics of such vortex pairs. In particular we simulate numerically the head-on collision of two pairs with different velocities for a wide range of the total linear momentum of the system. If the momentum difference of the two pairs is small, the vortices exchange partners, scatter at an angle depending on this difference, and form two new identical pairs. If it is large, the pairs pass through each other without losing their identity. We also study head-tail collisions. Two identical pairs moving in the same direction are bound into a moving quadrupole in which the two vortices as well as the two antivortices rotate around each other. We study the scattering processes also analytically in the frame of a collective variable theory, where the equations of motion for a system of four vortices constitute an integrable system. The features of the different collision scenarios are fully reproduced by the theory. We finally compare some aspects of the present soliton scattering with the corresponding situation in one dimension. Received 18 September 2001     

Formation and stability of coreless vortex dipoles in phase-separated binary condensates

We study the motion of the Gaussian obstacle potential created by a blue detuned laser beam through a phase-separated binary condensate in the pancake-shaped traps. We show that phase-separated binary condensates like ⁸⁵Rb–⁸⁷Rb, with appropriate interaction parameters, can be used experimentally to create obstacle assisted droplet and coreless vortex dipoles. We theoretically analyze the energetic stability of condensates with normal and coreless vortices. We confirm our analytic and semi-analytic results by numerical solutions of coupled Gross–Pitaevskii equations.     

圆管潜射流生成偶极子涡特性实验

利用溢流恒压装置产生具有稳定出流速度的圆管潜射流, 结合染色液流态显示方法, 在多种射流无量纲潜深d/H、雷诺数Re以及限制数C的组合下, 实验研究了该潜射流动量在有限深密度均匀流体中的演化特性, 其中d为射流潜深, H为水深. 研究表明, 当C<1时潜射流表现为深水特征, 而当1≤ C<2时潜射流表现为过渡特征, 在这两种情况下均不产生任何形式的大尺度相干结构; 当2≤ C<10时潜射流表现为浅水特征, 而C≥10时潜射流表现为极浅水特征, 在这两种情况下均产生大尺度的偶极子涡结构. 对极浅水特征潜射流, 在各种无量纲潜深下, 偶极子涡结构的无量纲形成时间t_f^*与无量纲射流时间T_inj^*均满足相同的正比例关系; 对浅水特征潜射流, 当d/H=0.5时, t_f^*与T_inj^*满足某种线性关系, 但对其他无量纲潜深, t_f^*与T_inj^*之间无明显规律. 关键词： 圆管潜射流 限制数 偶极子涡结构 形成时间     

Rotating vortex solitons supported by localized gain

We show that ringlike localized gain landscapes imprinted in focusing cubic (Kerr) nonlinear media with strong two-photon absorption support new types of stable higher-order vortex solitons containing multiple phase singularities nested inside a single core. The phase singularities are found to rotate around the center of the gain landscape, with the rotation period being determined by the strength of the gain and the nonlinear absorption.     

Cycloidal vortex motion in easy-plane ferromagnets due to interaction with spin waves

The dynamics of a non-planar vortex in a two-dimensional easy-plane ferromagnet of finite size is studied. Spin dynamics simulations show small cycloidal oscillations of the vortex around its mean path. In contrast to an earlier phenomenological theory we give a physical explanation: The oscillations occur due to the interaction of the vortex with coherent spin waves which are excited by this vortex at the moment when it starts to move, in order to conserve the total energy and angular momentum. The calculation of these quantities yields the frequencies and amplitudes of the cycloidal oscillations in good agreement with the simulation data. Received 9 December 2002 Published online 4 June 2003 RID="a" ID="a"e-mail: franz.mertens@uni-bayreuth.de     

Appearance of fractional vortex dipoles by using spiral linear zone plate

We present a novel technique based on linear zone plate (LZP) by which linear singularities regarded as fractional vortex dipoles are efficiently generated. Our approach requires applying spiral phase to a LZP, so fractional vortex dipoles are then acquired. By also implementing transverse phase shift to the spiral LZP, we are able to equally divide the number of the produced dark beams carrying mixed phase dislocations into two transverse separate parts. As a result, by varying a so called the controlling parameter the lateral positions of the focused fractional vortex dipoles are changed. Since we are able to generate dark beams in different and specific linear positions, therefore we suggest these features will be of great interest in one-dimensional optical trapping. All results are completely verified by experimental works.     

Steady motion of the magnetic vortex under the magnus force in weak ferromagnets

The problem of steady motion of the magnetic vortex in a moving domain wall under the action of the Magnus force in weak ferromagnets was studied. Dynamic bending of the domain wall containing a moving vortex was analyzed. The formulas describing the dependences of the vortex velocity on the velocity of the domain wall in which it moves were derived.     

Ionic dipoles in helium

Attention has been focused on the apparent indications of the existence of ionic dipoles in solid helium. The presence of identical quasiparticles in cryogenic liquids with a positive scattering length of embedded electrons has been suggested. Possible manifestations have been discussed, which would allow the detection of the gas of dipolar structures in superfluid helium and the investigation of its behavior.     

Spiral vortices in ferromagnets

New types of magnetic defects in two-dimensional ferromagnets are found in the exchange approximation, and the influence of magnetic anisotropy on their structure is analyzed.     

Magnetization concavity in ferromagnets

We investigate the conjecture that in Ising ferromagnets, single-site magnetization 〈σ _n 〉 is a jointly concave function of the magnetic field variables. We present partial results favoring the conjecture, including a numerical survey, although we do not prove it in full generality. We also point out some implications of concavity.     

Isotope effect in ferromagnets

A phenomenological approach to the theory of the isotope effect in ferromagnets is developed on the basis of the phenomenon of magnetoelasticity. Parameters whose experimental measurement permits a quantitative calculation of the contribution of acoustic phonons to the isotope shift of the Curie temperature are identified. An estimate of the isotope shift of the Curie temperature in the Invar alloy Fe_0.75Pt_0.25 is given. Zh. éksp. Teor. Fiz. 112, 1863–1872 (November 1997)     

Rotating Bose-Einstein condensate in an optical lattice: Formulation of vortex configuration for the ground state

We consider a rotating Bose-Einstein condensate in an optical lattice in the regime in which the system Hamiltonian can be mapped onto a Josephson junction array. In an approximate scheme where the couplings are assumed uniform, the ground state energy is formulated in terms of the vortex configuration. Application of the method for the ladder case presented and the results are compared with Monte-Carlo method.     

Domain wall dynamics in ferromagnets

The main results of studying the linear and nonlinear dynamics of a domain wall in ferromagnets are presented beginning with the first publications. The experimental data obtained on polycrystals, single crystals, and films differing in terms of their anisotropy, as well as on magnetic nanostructures, are compared with theoretical results obtained by various methods.     

Magnetostatic interface waves in ferromagnets

We derive the dispersion relation for magnetostatic surface waves guided by the interface between two ferromagnets. The applied field and saturation magnetization are parallel to the interface. The propagation of surface waves parallel to the interface is nonreciprocal and is limited to a restricted set of directions. An analytical expression is found for the critical angle, beyond which propagation is not allowed.     

Planar hall effect in ferromagnets

The planar Hall effect in a ferromagnetic conductor is considered within a simple two-liquid hydro-dynamic model. It is shown that, even in the simple case of an isotropic Fermi surface in the absence of thermal spread, the magnitude of the Hall effect is comparable to that in semiconductors because of the presence of two groups of conduction electrons with their spins parallel and perpendicular to the quantization axis, respectively. In addition to the planar Hall field, a spin flux parallel to this field arises, with the consequence that the extent of spin polarization of the conduction electrons varies along the Hall field direction (planar spin Hall effect).     

Spin waves in quantum ferromagnets

Low-temperature properties of Heisenberg quantum ferromagnets (spin waves) are derived within aconfiguration space formalism. Most of the work is done without explicitly assuming translational invariance. We provide a general criterion, classical domination, to decide about the nature and uniqueness of ground states for a large class of quantum ferromagnets. We also analyze and clarify the Dyson formalism and indicate why an energy gap between the physical ground state and the improper (unphysical) states does not exist. This is of particular relevance to the kinematical interaction. Using reflection positivity we provide upper and lower bounds to the contribution of the dynamical interaction to the free energy. In a certain approximation, these bounds imply that the dynamical interaction may be dropped if the inverse temperature and the spin quantum numberS are large enough.Suported in part by FAPESP.Supported in part by CAPES.Partial support by FAPESP and CNPq.