Giant Skyrmions stabilized by dipole-dipole interactions in thin ferromagnetic films

Motivated by a recent magnetization reversal experiment on a TbFeCo thin film, we study a topological excitation in the anisotropic nonlinear sigma model together with the Zeeman and magnetic dipole-dipole interactions. Dipole-dipole interactions turn a ferromagnet into a frustrated spin system, which allows a nontrivial spin texture such as a giant Skyrmion. We derive an analytic formula for the Skyrmion radius. The radius is controllable by the external magnetic field. It is intriguing that a Skyrmion may have already been observed as a magnetic domain. A salient feature is that a single Skyrmion can be created or destroyed experimentally. An analysis is made also on Skyrmions in chiral magnets.     

Weak Skyrmions and sphalerons

When the gauged non-linear -model is supplemented by a Skyrme term stable as well as unstable classical solutions exist: weak Skyrmions and sphalerons. Without the Skyrme term there remains only a sequence of sphalerons, which can be continued to finite Higgs masses. Here we investigate a model containing both, a finite Higgs mass and a Skyrme term. Stable weak Skyrmion solutions occur only above critical values of the Higgs mass and the Skyrme coupling constant.     

Weak Skyrmions and sphalerons

Recently proposed Skyrmion-like ansätze solve the field equations of the gauged non-linear sigma model. However, they are not classical solutions of the Weinberg-Salam model with finite Higgs coupling constant λ, where the only spherically symmetric solution is the hedgehog sphaleron.     

Homotopy of rational maps and the quantization of Skyrmions

The Skyrme model is a classical field theory which models the strong interaction between atomic nuclei. It has to be quantized in order to compare it to nuclear physics. When the Skyrme model is semi-classically quantized it is important to take the Finkelstein-Rubinstein constraints into account. The aim of this paper is to show how to calculate these FR constraints directly from the rational map ansatz using basic homotopy theory. We then apply this construction in order to quantize the Skyrme model in the simplest approximation, the zero mode quantization. This is carried out for up to 22 nucleons and the results are compared to experiment.     

On the global behaviour of symmetric Skyrmions

It is shown that the chiral angle, (r), of the hedgehog (symmetric) Skyrmions with an arbitrary baryon number, is a strictly decreasing or increasing function. For large values of r>0, (r) is strictly convex or concave. As r, (r) and (r) approach their limit values at the rate Or ^- for any (0,2).     

Intercommutation of semilocal strings and Skyrmions

We study the intercommuting of semilocal strings and Skyrmions for a wide range of internal parameters, velocities, and intersection angles by numerically evolving the equations of motion. We find that the collisions of strings and strings, strings and Skyrmions, and Skyrmions and Skyrmions all lead to intercommuting for a wide range of parameters. Even the collisions of unstable Skyrmions and strings lead to intercommuting, demonstrating that the phenomenon of intercommuting is very robust, extending to dissimilar field configurations that are not stationary solutions. Even more remarkably, at least for the semilocal U(2) formulation considered here, all intercommutations trigger a reversion to Nielsen-Olesen strings.     

Skyrmions in the quantum Hall effect and noncommutative solitons

It has been recently shown that solitons are fundamental classical solutions of non-commutative field theories. We reconsider this issue from the standpoint of the Hall effect and identify some solutions with known solutions in the integer Hall effect with no Zeeman coupling.     

Regular and Black Hole Skyrmions with Axisymmetry

It has been known that a B=2 skyrmion is axially symmetric. We consider the Skyrme model coupled to gravity and obtain static axially symmetric regular and black hole solutions numerically. Computing the energy density of the skyrmion, we discuss the effect of gravity to the energy density and baryon density of the skyrmion.     

Quark multiplets and their interactions

We investigate the potentials between static quark clusters in various SU(3)-representations below and above the deconfinement phase transition. In the confinement regime we are able to resolve in addition to the triplet-antitriplet system the triplet-sextet, the sextet-antisextet, and the octet-octet interactions at small distances. We give an explanation of the general laws for the interaction of quark clusters which have been found earlier. In the deconfinement regime we study multiplet-multiplet systems up to decuplets with high resolution. The energies at zero and infinite distance are determined by the Casimir operators.     

磁性多层膜中斯格明子的前景与挑战

拓扑磁学是近年内磁学领域内衍生出的一个子学科,它以寻找、研究和利用磁性材料中的拓扑自旋结构为核心目标,相关研究在凝聚态物理领域内已成为一个较大的分支。这些拓扑自旋结构包括：磁涡旋(magnetic vortex)、磁性斯格明子(magnetic skyrmion)、磁浮子(magnetic bobber)等。文章将以磁性多层膜中的斯格明子为对象,从材料优化、拓扑物理、表征、操控、探测等角度出发,详细讨论当前的主要研究热点,以及未来功能器件应用方面的一些挑战。