Multi-types of Skyrmions in SU(N) Quantum Hall System

The skyrmions in SU(N) quantum Hall (QH) system are discussed. By analyzing the gauge field structure and the topological properties of this QH system it is pointed out that in the SU( N) QH system there can exist ( N - 1)types of skyrmion structures, instead of only one type of skyrmions. In this paper, by means of the Abelian projections according to the (N - 1) Cartan subalgebra local bases, we obtain the (N - 1) U(1) electromagnetic field tensors in the SU(N) gauge field of the QH system, and then derive (N - 1) types of skyrmion structures from these U(1) sub-field tensors. Furthermore, in light of the φ-mapping topological current method, the topological charges and the motion of these skyrmions are also discussed.     

Skyrmion Excitations in Planar Ferromagnets

By making use of the C-mapping topological current theory and the decomposition of gauge potential theory, we investigate the （2＋1）-dimensional skyrmion excitations in ferromagnets. We also discuss the branch processes of these skyrmions and the generation and annihilation of skyrmion-antiskyrmion pairs.     

Vector and Spinor Decomposition of SU（2） Gauge Potential, Their Equivalence, and Knot Structure in SU（2） Chern-Simons Theory

In this paper, spinor and vector decompositions of SU（2） gauge potential are presented and their equivalence is constructed using a simply proposal. We also obtain the action of Faddeev nonlinear 0（3） sigma model from the SU（2） mass/ve gauge field theory, which is proposed according to the gauge invariant principle. At last, the knot structure in SU（2） Chern-Simons filed theory is discussed in terms of the Φ-mapping topological current theory, The topological charge of the knot is characterized by the Hopf indices and the Brouwer degrees of Φ-mapping.     

Gauge Model Based on Group G×SU（2）

We present a model of gauge theory based on the symmetry group G×SU（2） where G is the gravitational gauge group and SU（2） is the internal group of symmetry. We employ the spacetime of four-dimensional Minkowski, endowed with spherical coordinates, and describe the gauge fields by gauge potentials. The corresponding strength field tensors are calculated and the field equations are written. A solution of these equations is obtained for the case that the gauge potentials have a particular form potentials induces a metric of Schwarzschild type on with spherical symmetry. The solution for the gravitational the gravitational gauge group space.     

Vortex Lines and Monopoles in Electrically Conducting Plasmas

Based on the φ-mapping topological current theory and the decomposition of gauge potential theory, the vortex lines and the monopoles in electrically conducting plasmas are studied. It is pointed out that these two topological structures respectively inhere in two-dimensional and three-dimensional topological currents, which can be derived from the same topological term n^→·（Эin^→×Эjn^→）, and both these topological structures axe characterized by the φ-mapping topological numbers-Hopf indices and Brouwer degrees. Furthermore, the spatial bifurcation of vortex lines and the generation and annihilation of monopoles are also discussed. At last, we point out that the Hopf invaxiant is a proper topological invaxiant to describe the knotted solitons.     

Topological Defects in Liquid Crystal Films

A topological theory of liquid crystal films in the presence of defects is developed based on the Ф-mapping topological current theory. By generalizing the free-energy density in ＂one-constant＂ approximation, a covariant free- energy density is obtained, from which the U（1） gauge field and the unified topological current for monopoles and strings in liquid crystals are derived. The inner topological structure of these topological defects is characterized by the winding numbers of Ф-mapping.     

Topological Aspects in an Interacting Mixture of a Charged and a Neutral Superfluid in Neutron Stars

By making use of the decomposition of U（1） gauge potential theory and the C-mapping method we discuss a mixture of interacting neutral and charged Bose condensates, which is supposed to be realized in the interior of neutron stars in the form of a coexistent neutron superfluid and protonie superconductor. We propose that this system possesses vortex line knotted solitons and the topological charges of vortex lines are characterized by the winding numbers of the C-mapping. Furthermore the spatial bifurcation of vortices is also discussed.     

Self-dual Vortices in Schroedinger-Chern-Simons Model

By making use of the U（1） gauge potential decomposition theory and the Ф-mapping topological current theory, we investigate the Schroedinger-Chern-Simons model in the thin-film superconductor system and obtain an exact Bogomolny self-dual equation with a topological term. It is revealed that there exist self-dual vortices in the system. We study the inner topological structure of the self-dual vortices and show that their topological charges are topologically quantized and labeled by Hopf indices and Brouwer degrees. Furthermore, the vortices are found generating or annihilating at the limit points and encountering, splitting or merging at the bifurcation points of the vector field Ф.     

The Topological Structure of the SU（2） Chern-Simons Topological Current in the Four-Dimensional Quantum Hall Effect

In the light of the decomposition of the SU（2） gauge potential for I = 1/2, we obtain the SU（2） Chern-Simons current over S4, i.e. the vortex current in the effective field for the four-dimensional quantum Hall effect. Similar to the vortex excitations in the two-dimensional quantum Hall effect （2D FQH） which are generated from the zero points of the complex scalar field, in the 4D FQH, we show that the SU（2） Chern-Simons vortices are generated from the zero points of the two-component wave functions ψ, and their topological charges are quantized in terms of the Hopf indices and Brouwer degrees of Ф-mapping under the condition that the zero points of field ψ are regular points.     

Manipulating Skyrmion Motion on a Nanotrack with Varied Material Parameters and Tilted Spin Currents

Magnetic skyrmions are topological quasiparticles with nanoscale size and high mobility, which have potential applications in information storage and spintronic devices. The manipulation of skyrmion’s dynamics in the track is an important topic due to the skyrmion Hall effect, which can deviate the skyrmions from the preferred direction. We propose a new model based on the ferromagnetic skyrmion, where the skyrmion velocity can be well controlled by adjusting the direction of the current. Using ...     

磁斯格明子拓扑特性及其动力学微磁学模拟研究进展

具有非平庸拓扑性的新型磁结构斯格明子,由于其拓扑稳定性、尺寸小、低电流驱动等方面的显著优势,有望应用于自旋电子学储存器件.拓扑和凝聚态物理学的结合,使得斯格明子展现出很多有趣的拓扑物理现象,吸引了众多的研究兴趣,同时这些性质也是其电流驱动下动力学特点的重要影响因素.本文从斯格明子的拓扑物理学基础及其自旋电子学器件应用相关动力学两个方面介绍了相关研究进展.在拓扑物理基础方面,介绍了斯格明子的拓扑霍尔效应、斯格明子霍尔效应以及自旋轨道转矩等拓扑性质,由此讨论了斯格明子的动力学性质及其计算方法;在动力学方面,从非均匀电流驱动生成斯格明子、电流驱动下的稳定输运、产生湮灭过程的人工控制几个赛道存储应用关心的问题简要地介绍了相关微磁学模拟研究最新进展.     

磁性斯格明子的研究现状和展望

磁性斯格明子是具有拓扑保护性质的纳米尺度涡旋磁结构.斯格明子主要存在于非中心对称的手性磁性材料以及界面镜面对称性破缺的磁性薄膜材料中.因具有实空间的非平庸拓扑性,磁性斯格明子展现出丰富新奇的物理学特性,例如拓扑霍尔效应,新兴电磁动力学等,为研究拓扑自旋电子学提供了新的平台.另一方面,由于其具有尺寸小,高稳定性和易操控的特性,磁性斯格明子在未来高密度,低能耗,非易失性计算和存储器件中也具有潜在应用.现阶段的研究已经初步发现一系列磁斯格明子材料,并证明能够通过电流操控室温下稳定的磁性斯格明子,但是室温下单个斯格明子的精确产生、湮灭以及探测在实验上仍具有挑战性.本文阐述了磁性斯格明子的基础理论以及动力学研究现状,并对现有的斯格明子材料和斯格明子的产生,湮灭以及探测方法进行了总结,最后还对未来磁性斯格明子的物理理论研究以及应用发展中的挑战和机遇进行了讨论.     

磁性斯格明子的多场调控研究

斯格明子(skyrmion)的概念最早是由英国的粒子物理学家Tony Skyrme提出,它被用来描述粒子的一个状态,是一种拓扑孤立子.磁性斯格明子是一种具有拓扑行为的新型磁结构,其空间尺寸为纳米量级,空间距离从纳米到微米量级可调;其存在温度涵盖从低温、室温到高温的宽温区;其材料体系不仅包括早期发现的低温区B20型中心对称破缺的铁磁体和螺旋磁有序的弱铁磁材料,也包括近期发现的室温及以上的中心对称六角结构磁性MnNiGa金属合金和磁性薄膜/多层膜体系.利用磁性斯格明子的拓扑磁结构可以实现类似于自旋阀或者磁性隧道结中的自旋转移矩效应,即外加电流可以驱动斯格明子,其临界电流密度比传统翻转磁性多层膜体系中磁矩的电流密度(一般为10~7A/cm~2)要低5个数量级,约为10~2A/cm~2,该临界值远低于硅基半导体技术中沟道电流密度的上限,在未来的磁信息技术中具有广泛的应用前景.本综述简单介绍了磁性斯格明子的发展历程,归纳总结了磁性斯格明子的材料体系,介绍了观察磁性斯格明子的实验手段,重点介绍了多场(磁场、电流、温度场)调控作用下中心对称MnNiGa合金和Pt/Co/Ta磁性多层膜体系中磁性斯格明子的产生、消失以及外场调控演变等动态行为.     

Rotating skyrmions of the (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term

The (2 + 1)-dimensional Skyrme gauge model with a Chern-Simons term is considered. The presence of the Chern-Simons term makes possible the existence of two-dimensional skyrmions in this model, which carry magnetic flux and have an electric charge and a nonzero angular momentum. It is shown that the model also admits the existence of two-dimensional skyrmions with a nonzero phase frequency of rotation. Due to the nontrivial topological properties of the model, the magnetic flux, the electric charge, and the angular momentum of a two-dimensional rotating skyrmion turn out to be interrelated. Analytic and numerical investigations of the properties of rotating two-dimensional skyrmions are carried out.     

磁畴壁手性和磁斯格明子的拓扑性表征及其调控

磁性斯格明子由于拓扑的保护性,具有很高的稳定性和较小的临界驱动电流,有望应用于未来的赛道存储器件中.而在中心对称体系,由于偶极作用的各向同性,磁泡的拓扑性和螺旋度都呈现出多样性的特征.其中非平庸的磁泡即等同于磁性斯格明子.我们通过近期实验结果,结合微磁学模拟的方法,发现在中心对称体系中磁斯格明子的拓扑性会受到体系垂直各向异性的调控.另外在加磁场的演变过程中,会很大程度上依赖于基态畴的畴壁特性.磁场的倾斜或者一定的面内各向异性也会改变磁斯格明子的形态.通过对材料的基态磁结构及磁各向异性的调节,辅助以面内分量的控制,可以对基态磁畴、进而对磁斯格明子的拓扑性实现调控.这对磁斯格明子在电流驱动存储器件中的应用具有重要意义.     

Non-volatile multi-state magnetic domain transformation in a Hall balance

High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered as a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (a SAF with the core structure of [Co/Pt]₄/NiO/[Co/Pt]₄ showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.     

Progress and challenges in magnetic skyrmionics

Magnetic skyrmions are two-dimensional localized topological spin-structures characterized by the skyrmion number that measures the number of times of spins wrapping the Bloch sphere. Skyrmions behave like particles under an external stimulus and are promising information carriers. Skyrmions can exist as an isolated object as well as skyrmion condensates in crystal structures, helical/conical states, mazes or irregular stripy states with emergent electromagnetic fields. Thus, skyrmions provide a nice platform for studying fundamental physics, other than its applications in spintronics. In this perspective, we briefly review some recent progress in the field and present an outlook of the fundamental challenges in device applications.     

Topological charge analysis of dynamic process of transition to Néel-type skyrmion: Role of domain wall skyrmions

Magnetic skyrmions are intriguing topological spin textures that promise future high-density spintronic devices. The creation of magnetic skyrmions has been understood based on the energetics of skyrmions, but the detailed dynamic process of the skyrmion creation remains unclear. Here topological evolution in conversion from uneven domains to Néel-skyrmions is investigated using micromagnetic simulations. We find that, rather than the overall topological charge, annihilation of novel topological defects, i.e., recently suggested domain wall skyrmions, dominantly govern the skyrmion creation process. Also, the topological charge evolution is interpreted in terms of the number and the combination of such topological defects.