arXiv subjects

Martin Speight

Publications and source records attributed to Martin Speight.

29 records · Page 2Linked to original sources

arXiv2013

Isospinning hopfions

The problem of constructing internally rotating solitons of fixed angular frequency $ω$ in the Faddeev-Skyrme model is reformulated as a variational problem for an energy-like functional, called pseudoenergy, which depends parametrically on $ω$. This problem is solved numerically using a gradient descent method, without imposing any spatial symmetries on the solitons, and the dependence of the solitons' energy on $ω$, and on their conserved total isospin $J$, studied. It is found that, generically, the shape of a soliton is independent of $ω$, and that its size grows monotonically with $ω$. A simple elastic rod model of time-dependent hopfions is developed which, despite having only one free parameter, accounts well for most of the numerical results.

hep-th↗

arXiv2013

Chiral CP^2 skyrmions in three-band superconductors

It is shown that under certain conditions, three-component superconductors (and in particular three-band systems) allow stable topological defects different from vortices. We demonstrate the existence of these excitations, characterized by a $CP^2$ topological invariant, in models for three-component superconductors with broken time reversal symmetry. We term these topological defects "chiral $GL^{(3)}$ skyrmions", where "chiral" refers to the fact that due to broken time reversal symmetry, these defects come in inequivalent left- and right-handed versions. In certain cases these objects are energetically cheaper than vortices and should be induced by an applied magnetic field. In other situations these skyrmions are metastable states, which can be produced by a quench. Observation of these defects can signal broken time reversal symmetry in three-band superconductors or in Josephson-coupled bilayers of $s_\pm$ and s-wave superconductors.

cond-mat.supr-con↗

arXiv2011

Broken Baby Skyrmions

The baby Skyrme model is a (2+1)-dimensional analogue of the Skyrme model, in which baryons are described by topological solitons. In this paper we introduce a version of the baby Skyrme model in which the global O(3) symmetry is broken to the dihedral group D_N. It is found that the single soliton in this theory is composed of N partons, that are topologically confined. The case N=3 is studied in some detail and multi-soliton solutions are computed. These soliton solutions are related to polyiamonds, which are plane figures composed of equilateral triangles joined by common edges. It is shown that the solitons may be viewed as pieces of a doubly periodic soliton lattice. An alternative model with D_3 symmetry is also introduced, which has an exact explicit soliton lattice solution. Soliton solutions are computed and compared in the two D_3 theories. Some comments are made regarding the extension of these ideas to the Skyrme model.

hep-th↗

arXiv2011

Type-1.5 superconductivity in multiband systems: the effects of interband couplings

In contrast to single-component superconductors, which are described at the level of Ginzburg-Landau theory by a single parameter κand are divided in type-I κ<1/\sqrt{2} and type-II κ>1/\sqrt{2} classes, two-component systems in general possess three fundamental length scales and have been shown to possess a separate "type-1.5" superconducting state. In that state, as a consequence of the extra fundamental length scale, vortices attract one another at long range but repel at shorter ranges, and therefore should form clusters in low magnetic fields. In this work we investigate the appearance of type-1.5 superconductivity and the interpretation of the fundamental length scales in the case of two bands with substantial interband couplings such as intrinsic Josephson coupling, mixed gradient coupling and density-density interactions. We show that in the presence of substantial intercomponent interactions of the above types the system supports type-1.5 superconductivity with fundamental length scales being associated with the mass of the gauge field and two masses of normal modes represented by mixed combinations of the density fields.

cond-mat.supr-con↗

arXiv2011

Easy plane baby skyrmions

The baby Skyrme model is studied with a novel choice of potential, $V=1/2 ϕ_3^2$. This "easy plane" potential vanishes at the equator of the target two-sphere. Hence, in contrast to previously studied cases, the boundary value of the field breaks the residual SO(2) internal symmetry of the model. Consequently, even the unit charge skyrmion has only discrete symmetry and consists of a bound state of two half lumps. A model of long-range inter-skyrmion forces is developed wherein a unit skyrmion is pictured as a single scalar dipole inducing a massless scalar field tangential to the vacuum manifold. This model has the interesting feature that the two-skyrmion interaction energy depends only on the average orientation of the dipoles relative to the line joining them. Its qualitative predictions are confirmed by numerical simulations. Global energy minimizers of charges B=1,...,14,18,32 are found numerically. Up to charge B=6, the minimizers have 2B half lumps positioned at the vertices of a regular 2B-gon. For charges B >= 7, rectangular or distorted rectangular arrays of 2B half lumps are preferred, as close to square as possible.

hep-th↗

arXiv2010

Type-1.5 Superconducting State from an Intrinsic Proximity Effect in Two-Band Superconductors

We show that in multiband superconductors even small interband proximity effect can lead to a qualitative change in the interaction potential between superconducting vortices by producing long-range intervortex attraction. This type of vortex interaction results in unusual response to low magnetic fields leading to phase separation into domains of a two-component Meissner states and vortex droplets.

cond-mat.supr-con↗

arXiv2010

Hopf solitons and elastic rods

Hopf solitons in the Skyrme-Faddeev model are string-like topological solitons classified by the integer-valued Hopf charge. In this paper we introduce an approximate description of Hopf solitons in terms of elastic rods. The general form of the elastic rod energy is derived from the field theory energy and is found to be an extension of the classical Kirchhoff rod energy. Using a minimal extension of the Kirchhoff energy, it is shown that a simple elastic rod model can reproduce many of the qualitative features of Hopf solitons in the Skyrme-Faddeev model. Features that are captured by the model include the buckling of the charge three solution, the formation of links at charges five and six, and the minimal energy trefoil knot at charge seven.

hep-th↗

arXiv2009

Magnetic field delocalization and flux inversion in fractional vortices in two-component superconductors

We demonstrate that, in contrast to the single-component Abrikosov vortex, in two-component superconductors vortex solutions with exponentially screened magnetic field exist only in exceptional cases: in the case of vortices carrying an integer number of flux quanta, and in a special parameter limit for half-quantum vortices. For all other parameters the vortex solutions have delocalized magnetic field with a slowly decaying tail. Furthermore, we demonstrate a new effect which is generic in two-component systems but has no counterpart in single-component systems: on exactly half of the parameter space of the $U(1)\times U(1)$ Ginzburg-Landau model, the magnetic field of a generic fractional vortex inverts its direction at a certain distance from the vortex core.

cond-mat.supr-con↗

arXiv2009

Exact moduli space metrics for hyperbolic vortices

Exact metrics on some totally geodesic submanifolds of the moduli space of static hyperbolic N-vortices are derived. These submanifolds, denoted Σ_{n,m}, are spaces of C_n-invariant vortex configurations with n single vortices at the vertices of a regular polygon and m=N-n coincident vortices at the polygon's centre. The geometric properties of Σ_{n,m} are investigated, and it is found that Σ_{n,n-1} is isometric to the hyperbolic plane of curvature -1/(3πn). Geodesic flow on Σ_{n,m}, and a geometrically natural variant of geodesic flow recently proposed by Collie and Tong, are analyzed in detail.

hep-th↗

arXiv2005

Fermionic quantization of Hopf solitons

In this paper we show how to quantize Hopf solitons using the Finkelstein-Rubinstein approach. Hopf solitons can be quantized as fermions if their Hopf charge is odd. Symmetries of classical minimal energy configurations induce loops in configuration space which give rise to constraints on the wave function. These constraints depend on whether the given loop is contractible. Our method is to exploit the relationship between the configuration spaces of the Faddeev-Hopf and Skyrme models provided by the Hopf fibration. We then use recent results in the Skyrme model to determine whether loops are contractible. We discuss possible quantum ground states up to Hopf charge Q=7.

hep-th↗

arXiv2004

Fermionic quantization and configuration spaces for the Skyrme and Faddeev-Hopf models

The fundamental group and rational cohomology of the configuration spaces of the Skyrme and Faddeev-Hopf models are computed. Physical space is taken to be a compact oriented 3-manifold, either with or without a marked point representing an end at infinity. For the Skyrme model, the codomain is any Lie group, while for the Faddeev-Hopf model it is $S^2$. It is determined when the topology of configuration space permits fermionic and isospinorial quantization of the solitons of the model within generalizations of the frameworks of Finkelstein-Rubinstein and Sorkin. Fermionic quantization of Skyrmions is possible only if the target group contains a symplectic or special unitary factor, while fermionic quantization of Hopfions is always possible. Geometric interpretations of the results are given.

hep-th↗