Possibility of two-stage flux penetration in antiferromagnetic superconductors

An induced ferromagnetism in antiferromagnetic superconductors is possible, caused by a magnetic structure of vortex lines appearing in an external magnetic field strong enough to “flip over” the spins in the vortex core from their antiferromagnetic configuration. If the magnetic field is less than the “flip over” field the vortex line is entirely in the antiferromagnetic phase. Therefore the vortex interaction with the surface of a sample is altered when an applied magnetic field exceeds the “flip over” field. This mechanism makes the appearance of a new energy barrier that strongly influences the flux penetration possible. An estimation of the second critical entry field is made for DyMo₆S₈.     

Inverted satellites of a solitary oscillating pearl vortex in a thin magnetic superconductor film

An electrodynamic equation is derived for the magnetic field of an isolated Pearl vortex moving along an arbitrary trajectory in an ultrathin film of a magnetic superconductor. This equation is valid for any type of magnetic order in the magnetic subsystem. The magnetic structure of an isolated oscillating Pearl vortex is investigated in a thin magnetic superconductor film. Oscillations of the vortex and the presence of the magnetic subsystem are shown to lead to a significant renormalization of the vortex field in comparison with the Pearl solution. New phenomena of inverted satellites are predicted in which an inverted precursor appears in front of the vortex and an inverted wake is formed behind the latter at a distance of the order of 10λ_eff from the vortex center. These phenomena can be observed in magnetooptical experiments.     

“Inversion wake” of an isolated moving Pearl vortex in a thin magnetic superconductor film

The magnetic structure of an isolated two-dimensional Pearl vortex uniformly moving in a thin magnetic superconductor film is studied. The moving process and the magnetic subsystem sizably renormalize the Pearl vortex field and induce the formation of an “inversion wake” behind the vortex at a large distance on the order of 10λ _eff from its center. The effect can be observed in the magneto-optical experiments.     

On the direction of the magnetic line and the circulating supercurrent of a vortex in type-II superconductors

The relationship between the direction of the magnetic line and the circulating supercurrent of a vortex in type-II superconductors is discussed. Contrary to the views presented in some articles, we will make it clear that the magnetic line and the circulating supercurrent of a vortex have a “right hand” relationship by considering basic electrodynamics and the lowest energy principle.     

Vortices and magnetic structures of the target type in a two-dimensional ferromagnet with anisotropic exchange

Various types of magnetic structure in a two-dimensional Heisenberg ferromagnet are considered in a continuum approximation. The effect of anisotropic exchange and single-ion anisotropy on the vortex structure is analyzed. A new type of static magnetic structure (“target”) is predicted and investigated in an easy-plane ferromagnet.     

Persistent currents and magnetization in two-dimensional magnetic quantum systems

Persistent currents and magnetization are considered for a two-dimensional electron (or gas of electrons) coupled to various magnetic fields. Thermodynamic formulae for the magnetization and the persistent current are established and the “classical” relationship between current and magnetization is shown to hold for systems invariant both by translation and rotation. Applications are given, including the point vortex superposed onto an homogeneous magnetic field, the quantum Hall geometry (an electric field and an homogeneous magnetic field) and the random magnetic impurity problem (a random distribution of point vortices).     

Electric control of magnetic moment in a ferromagnet/semiconductor hybrid system

It is shown that the exchange coupling in a “ferromagnet/semiconductor quantum well” heterostructure allows the electric control of the orientation of magnetic moment in the ferromagnet. A highly anisotropic exchange interaction between holes in the quantum well and magnetic atoms in the ferromagnet causes the orientational transition: magnetic moment leaves the plane and becomes oriented along the normal. The normal component of magnetization can be inverted by applying voltage pulses to the structure gate.     

Transport phenomena of aligned ybco polycrystals near vortex-glass transition temperature in weak magnetic field

Abstract

Transport phenomena of aligned polycrystalline Y₁Ba₂Cu₃O_7?δ samples in weak magnetic fields near the vortex-glass transition temperature T_g have been studied. In YBCO polycrystal a fully superconducting state develops via an “intermediate phase”. The non-ohmic dissipation in this “intermediate phase” is examined in terms of both the thermal activated flux-flow (TAFF) model and vortex-glass transition model. Our experimental results in low magnetic fields can better be explained by a vortex glass transition model rather than a TAFF model. We have reinterpreted the non-ohmic dissipative region below T_c , i.e., the so-called “intermediate phase” in terms of a vortex-glass phase.     

On possibility of the spontaneous magnetic flux in a Josephson junction containing magnetic impurities

The Josephson junction containing localized magnetic moments in a dielectric layer between two superconductors is considered. Conditions are studied under which the phase difference between superconductors in the state with energy minimum is equal to π (such a junction we call π-junction). In addition we consider “one-dimensional” Josephson junction one part (2) of which is π-junction, the other (1) being the usual Josephson junction ( 0 - junction). Conditions are found under which in such a system there is a spontaneous vortex with the centre at the boundary between the parts 1 and 2 and magnetic flux associated with this vortex. The vortex appears by second order phase transition as temperature decreases for T_c.     

Mass of the higgs versus fourth generation masses

Double sign inversion of the topological charge of an optical vortex was predicted and observed experimentally for a beam focused by a cylindrical lens. Beam evolution after passing through the lens is analyzed by the decomposition of the orbital angular momentum into the “vortical” and “mechanical” components. Topological reactions in the beam wave resulting in the sign inversion of the optical vortex upon the intersection of the wave-front edge dislocation are considered.     

基于倾斜纳磁体翻转倾向性的与(或)逻辑门应力模型

纳米磁性逻辑器件具有高抗辐射性、低功率、天然非易失性等优势,应用前景广阔.倾斜放置的纳磁体具有翻转倾向性,在控制时钟撤去后倾斜纳磁体倾向于翻转至长轴的一端.利用倾斜纳磁体的翻转倾向性,提出了一种应力调控的与(或)磁逻辑门,并建立了其动态磁化的数学模型.使用微磁学方法对逻辑门进行了仿真,结果验证了预期逻辑门功能.与现有的逻辑门相比,基于倾斜纳磁体的与(或)门结构具有能耗更低、可靠性更高和制造工艺更简单等优点.     

Superfluid bosons and flux liquids: disorder,thermal fluctuations,and finite-size effects

The influence of different types of disorder (both uncorrelated and correlated) on the superfluid properties of a weakly interacting or dilute Bose gas, as well as on the corresponding quantities for flux line liquids in high-temperature superconductors at low magnetic fields are reviewed, investigated and compared. We exploit the formal analogy between superfluid bosons and the statistical mechanics of directed lines, and explore the influence of the different “imaginary time” boundary conditions appropriate for a flux line liquid. For superfluids, we discuss the density and momentum correlations, the condensate fraction, and the normal-fluid density as function of temperature for two- and three-dimensional systems subject to a space- and time-dependent random potential as well as conventional point-, line-, and plane-like defects. In the case of vortex liquids subject to point disorder, twin boundaries, screw dislocations, and various configurations of columnar damage tracks, we calculate the corresponding quantities, namely, density and tilt correlations, the “boson” order parameter, and the tilt modulus. The finite-size corrections due to periodic vs. open “imaginary time” boundary conditions differ in interesting and important ways. Experimental implications for vortex lines are described briefly.     

Three-Dimensional Numerical Simulation of Long-Lived Quantum Vortex Knots and Links in a Trapped Bose Condensate

The dynamics of the simplest vortex knots, “unknots,” and torus links in an atomic Bose condensate at zero temperature in an anisotropic harmonic trap has been simulated numerically within the three-dimensional Gross–Pitaevskii equation. It has been found that such quasistationary rotating vortex structures exist for a very long time in wide ranges of the parameters of the system. This new result is qualitatively consistent with a previous prediction based on a simplified one-dimensional model approximately describing the motion of knotted vortex filaments.     

YBa2Cu3O7-δ外延膜中的非线性光响应

实验结果表明，在连续波He-Ne激光(λ=0.63μm)照射下，YBa₂Cu₃O_7-δ(YBCO)外延膜在超导转变温度T_c以下附近温区的光响应行为，表现为辐射热效应和非辐射热效应同时存在，尤其当样品的R-T变化率dR/dT→0温区明显地表现为一种非平衡光响应行为，且随电流的变化呈非线性关系.基于上述实验事实，在光致准粒子激发假设下，对T_c附近YBCO薄膜中的非线性光响应机制进行了讨论；给出了光辐射 关键词：     

Interaction between a composite compression wave and a vortex in a thermodynamically nonideal medium

A numerical analysis is presented of two-dimensional interaction between a transverse vortex and a composite compression wave that can exist in a thermodynamically nonideal medium. It is shown that the interaction of a composite wave involving a “neutrally stable” shock with a vortex generates weakly damped outgoing acoustic waves; i.e., the shock is a source of sound. This phenomenon increases the post-shock acoustic noise level in an initially turbulent flow.     

Phase transitions in a two-dimensional vortex system with defects: Monte Carlo simulation

AbstractThe phase states and phase transitions in a system consisting of a two-dimensional vortex lattice with defects are studied by the Monte Carlo method. It is shown that a “rotating lattice” phase, which is an intermediate phase between the vortex crystal and vortex liquid phases, is present. The dependence of the temperature of the transition from the rotating lattice phase into a vortex liquid on the strength of the defect potential is determined. The current-voltage characteristics of the system are calculated at various temperatures for point, square, and linear defects. It is shown that the phase state of the system strongly affects its transport properties.     

Alteration of the ground state by external magnetic fields: The Abelian Higgs model

By fully exploiting the mathematical and physical analogy to the Ginzburg-Landau theory of superconductivity, we present a complete discussion of the ground state behavior of the four-dimensional Abelian Higgs model in the static tree level approximation. We show that a sufficiently strong external magnetic field can alter the ground state of the theory by restoring a spontaneously broken symmetry, or by creating a qualitatively different “vortex” state. The energetically favored ground state is explicitly determined as a function of the external field and the ratio between coupling constants of the theory.     

Two-dimensional matter-wave solitons and vortices in competing cubic-quintic nonlinear lattices

The nonlinear lattice — a new and nonlinear class of periodic potentials — was recently introduced to generate various nonlinear localized modes. Several attempts failed to stabilize two-dimensional (2D) solitons against their intrinsic critical collapse in Kerr media. Here, we provide a possibility for supporting 2D matter-wave solitons and vortices in an extended setting — the cubic and quintic model — by introducing another nonlinear lattice whose period is controllable and can be different from its cubic counterpart, to its quintic nonlinearity, therefore making a fully “nonlinear quasi-crystal”.A variational approximation based on Gaussian ansatz is developed for the fundamental solitons and in particular, their stability exactly follows the inverted Vakhitov–Kolokolov stability criterion, whereas the vortex solitons are only studied by means of numerical methods. Stability regions for two types of localized mode — the fundamental and vortex solitons — are provided. A noteworthy feature of the localized solutions is that the vortex solitons are stable only when the period of the quintic nonlinear lattice is the same as the cubic one or when the quintic nonlinearity is constant, while the stable fundamental solitons can be created under looser conditions. Our physical setting (cubic-quintic model) is in the framework of the Gross–Pitaevskii equation or nonlinear Schrödinger equation, the predicted localized modes thus may be implemented in Bose–Einstein condensates and nonlinear optical media with tunable cubic and quintic nonlinearities.     

Dynamics of and radiation from superconducting strings and springs

We present a detailed study of the dynamics of and radiation from superconducting strings. We derive an approximate local action for a current-carrying vortex line and present some exact solutions to its equation of motion. These include stable static “springs” and oscillating “kinky” loops. For one of these “kinky” loops we are able to calculate the radiation exactly, and find (in contrast to previous work) the result is finite. We also argue that the non-local electromagnetic self-interaction of a loop causes the kinks to slowly straighten out. Finally, we discuss the loss of current at “cusp-like” regions and show that the shrinking of loops generally leads to current loss rather than gain.