Periodic Néel skyrmion transport

In this work, we have used the MuMax3 software to simulate devices consisting of a ferromagnetic thin film placed over a heavy metal thin film. The devices are two interconnected partial-disks where a Néel domain wall is formed in the disks junction. In our simulations we investigate devices with disk radius $r=50$ nm and different distance d between the disks centers (from $d=12$ nm to $d=2R=100$ nm). By applying strong sinusoidal external magnetic fields, we find a mechanism able to create, annihilate and even manipulate a skyrmion in each side of the device. This mechanism is discussed in terms of interactions between skyrmion and domain wall. The Néel domain wall formed in the center of the device interacts with the Néel skyrmion, leading to a process of transporting a skyrmion from one disk to the other periodically. Our results have relevance for potential applications in spintronics such as logical devices.     

低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律

利用蒙特卡洛方法研究了低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律,以及偶极相互作用对螺旋磁体纳米条带中磁结构的影响。研究表明,螺旋磁体纳米条带中的自旋结构由自旋的面内取向平行或垂直于边界的边缘态和中间聚集态两部分构成。在一定范围内增加外磁场,条带边缘平行于边界的自旋排列将增多,最终将在条带外围形成大的磁涡旋环,该涡旋环十分稳定,即使在很强的外磁场下仍然存在。处于条带中间的聚集态随着外磁场的增大,从磁螺旋态逐步过渡到Skyrmions态,最终形成铁磁态。Skyrmions的排列状况与条带尺寸密切相关。此外,偶极相互作用对磁矩平行于边界且首尾顺次连接的排列起积极作用,在无外磁场作用下,随着偶极相互作用的增大,体系终将形成涡旋态。     

Quantum Hall skyrmions with higher topological charge

We have investigated quantum Hall skyrmions with more than one unit of topological, and hence electric, charge. Using a combination of analytic and numerical methods we find the counterintuitive result that when the Zeeman energy is tuned to values much smaller than the interaction energy ( ), the creation energy of a charge two skyrmion becomes less than twice the creation energy of a charge one skyrmion, i.e. skyrmions bind in pairs. The doubly charged skyrmions are stable to further accretion of charge and exhibit a larger spin per unit charge than charge one skyrmions which would, in principle, signal this pairing. 1997 Elsevier Science B.V. All rights reserved.     

Rational maps, monopoles and skyrmions

We discuss the similarities between BPS monopoles and skyrmions, and point to an underlying connection in terms of rational maps between Riemann spheres. This involves the introduction of a new ansatz for Skyrme fields. We use this to construct good approximations to several known skyrmions, including all the minimal energy configurations up to baryon number nine, and some new solutions such as a baryon number seventeen Skyrme field with the truncated icosahedron structure of a buckyball.

The new approach is also used to understand the low-lying vibrational modes of skyrmions, which are required for quantization. Along the way we discover an interesting Morse function on the space of rational maps which may be of use in understanding the Sen forms on the monopole moduli spaces.     

Bound-state versus collective-coordinate approaches in chiral soliton models and the width of the Θpentaquark

We thoroughly compare the bound-state and rigid-rotator approaches to three-flavored chiral solitons. We establish that these two approaches yield identical results for the baryon spectrum and kaon-nucleon S-matrix in the limit that the number of colors (N_C) tends to infinity. After proper subtraction of the background phase shift the bound-state approach indeed exhibits a clear resonance behavior in the strangeness S = + 1 channel. We present a first dynamical calculation of the widths of the Θ⁺ and Θ^* pentaquarks for finite N_C in a chiral soliton model.     

solitons in quantum Hall systems

We present here an elementary pedagogical introduction to CP_N solitons in quantum Hall systems. We begin with a brief introduction to both CP_N models and to quantum Hall (QH) physics. We then focus on spin and layer-spin degrees of freedom in QH systems and point out that these are in fact CP_N fields for N = 1 and N = 3. Excitations in these degrees of freedom will be shown to be topologically non-trivial soliton solutions of the corresponding CP_N field equations. We conclude with a brief summary of our own recent work in this area, done with Sankalpa Ghosh. Received 17 November 2001 Published online 2 October 2002 RID="a" ID="a"e-mail: doug0700@mail.jnu.ac.in     

低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律

利用蒙特卡洛方法研究了低维螺旋磁体纳米条带中磁场驱动的磁结构演变规律,以及偶极相互作用对螺旋磁体纳米条带中磁结构的影响。研究表明,螺旋磁体纳米条带中的自旋结构由自旋的面内取向平行或垂直于边界的边缘态和中间聚集态两部分构成。在一定范围内增加外磁场,条带边缘平行于边界的自旋排列将增多,最终将在条带外围形成大的磁涡旋环,该涡旋环十分稳定,即使在很强的外磁场下仍然存在。处于条带中间的聚集态随着外磁场的增大,从磁螺旋态逐步过渡到Skyrmions态,最终形成铁磁态。Skyrmions的排列状况与条带尺寸密切相关。此外,偶极相互作用对磁矩平行于边界且首尾顺次连接的排列起积极作用,在无外磁场作用下,随着偶极相互作用的增大,体系终将形成涡旋态。     

Low-Lying Pentaquark Baryons in Pseudoscalar-Vector SU(3) Skyrme Model

For the first time the low-lying J = 1/2 pentaquark states are investigated in the pseudoscalar-vector Skyrme model. Once the conventional baryon properties are fit, other states are predicted without any more adjustable parameters. Furthermore, both symmetry-breaking and decay operators are treated in full. In particular, we focus on the calculations of mass and decay width, and compare them with the experimental data available and relevant theoretical results obtained in other pictures. We recognize that the higher-order contributions, such as the 35 and/or (-35) representation admixtures, are not negligible. Our analysis provides some valuable clues to the physical mechanisms, and the oncoming experimental search and/or confirmation could provide a sharp test of our proposal.     

Strange and heavy flavoured hypernuclei in chiral soliton models

The extension of the chiral soliton approach to hypernuclei --strange or heavy flavoured-- becomes more reliable due to the success in describing other properties of nuclei, e.g. the symmetry energy of nuclei with atomic numbers up to ∼ 30 . The binding energies of the ground states of light hypernuclei with S = - 1 have been described in qualitative agreement with data. The existence of charmed or beautiful hypernuclei and Theta-hypernuclei (strange, charmed or beautiful) with large binding energy is expected within same approach.