arXiv subjects

Paul Leask

Publications and source records attributed to Paul Leask.

16 recordsLinked to original sources

arXiv2026

Ultrasound Evidence for a Low-Temperature Anomaly Inside the Superconducting State of 4Hb-TaS$_2$

We report low-temperature ultrasound measurements on single crystals of the layered van der Waals superconductor 4Hb-TaS$_2$. Specific heat and ac magnetic susceptibility show a sharp bulk superconducting transition at $T_{\rm c}\approx 2.9$~K. Ultrasound measurements reveal an additional anomaly deep inside the superconducting state near $T^{*}\approx 1$~K. The most direct signature is observed in the relative ultrasonic attenuation change $\Delta\alpha$: instead of being rapidly suppressed at $T_{\rm c}$, $\Delta\alpha$ remains large throughout the intermediate superconducting regime and drops strongly only near $T^{*}$. This loss of acoustic dissipation is accompanied by a pronounced anomaly in the relative sound velocity change $\Delta v/v$, indicating strong coupling to the lattice. The low-temperature anomaly is rapidly suppressed by magnetic field and by Se substitution, suggesting a possible superconducting origin of the anomaly. We speculate that this feature may be related to induced superconductivity in the 1T layers.

cond-mat.supr-con↗

arXiv2026

$\texttt{cuSkyrmion}$: A CUDA-OpenGL framework for interactive simulation and visualization of nuclei as Skyrmions

We introduce $\texttt{cuSkyrmion}$, a 3-dimensional Skyrme model computation and visualization software, that is written in $\texttt{CUDA C}$ for rapid computation and visualization of especially the arrested Newton flow algorithm. The programme is interactive and lets the user construct Skyrmions either with configuration files, specifying coordinates, or simply in run-time using the keyboard and mouse. Rational map ansatz constituent Skyrmions can be inserted at any time and a random generator can produce a stochastic initial configuration. The software is composed into three main modules being a computational module, a rendering module and a main programme. The rendering/visualization module can readily be used by other computational modules and a $\texttt{Python}$-fork, $\texttt{skyrmion_solver}$, has been developed demonstrating the re-usability of the code.

hep-ph↗

arXiv2026

soliton_solver: A GPU-based finite-difference PDE solver for topological solitons in two-dimensional non-linear field theories

This paper introduces soliton_solver, an open-source GPU-accelerated software package for the simulation and real-time visualization of topological solitons in two-dimensional non-linear field theories. The software is structured around a theory-agnostic numerical core implemented using Numba CUDA kernels, while individual physical models are introduced through modular theory components. This separation enables a single computational framework to be applied across a broad class of systems, from nanoscale magnetic spin textures in condensed matter physics to cosmic strings spanning galaxies in high energy physics. The numerical backend provides finite-difference discretization, energy minimization, and GPU-resident evaluation of observables. A CUDA--PyOpenGL rendering pipeline allows direct visualization of evolving field configurations without staging full arrays through host memory. The package is distributed in Python via PyPI and supports both reproducible batch simulations and interactive exploration of metastable configurations, soliton interactions, and model-dependent initial states. We describe the software architecture, numerical workflow, and extensibility model, and we present representative example applications. We also outline how additional theories can be incorporated with minimal modification of the shared numerical infrastructure.

hep-th↗

arXiv2026

Interactions of composite magnetic skyrmion-superconducting vortex pairs in ferromagnetic superconductors

We study composite topological excitations in ferromagnetic superconductors consisting of bound states of magnetic spin textures (skyrmions) and superconducting vortices. Using a Ginzburg--Landau framework with Zeeman coupling between the magnetization and superconducting magnetic field, we demonstrate that skyrmion-vortex pairs (SVPs) form energetically stable bound states. By analyzing their asymptotic interactions, we identify regimes in which SVPs exhibit both short-range repulsion and long-range attraction, leading to clustering phenomena. Our results provide a field-theoretical basis for understanding suggest pathways for controlling hybrid topological matter through long-range interactions.

cond-mat.supr-con↗

arXiv2025

Multiple correlation lengths and type-1.5 superconductivity in $U(1)$ superconductors due to hidden competition between irreducible representations of nonlocal pairing

A fundamental characteristic of a superconducting state is the coherence length $\xi$. Multicomponent superconductors, particularly ones breaking multiple symmetries, are characterized by multiple coherence lengths. Here we show that even, nominally $single$-component superconductors under certain conditions are characterized by multiple coherence lengths. We consider nearest-neighbor pairing interactions on a square lattice that leads to $s$-wave and $d$-wave representations of link superconducting order parameter. We show that even if the subdominant order parameter is completely suppressed in the ground state, it results in multiple correlation lengths with nontrivial hierarchy, resulting in important physical consequences in inhomogeneous solutions. Under certain conditions, this leads to type-1.5 superconductivity, where magnetic field penetration length falls between two coherence lengths, leading to vortex clustering in an external magnetic field.

cond-mat.supr-con↗

arXiv2025

Anyon Bound States and Hybrid Superconductivity

The interactions of anyonic quasi-particles (vortices) in the Chern--Simons extension of the Ginzburg--Landau model is investigated and we show that it manifestly realizes a hybridization of type I/II superconductivity. Through Gauss' law, each vortex simultaneously carries a flux quantum and a proportional Noether charge, thereby realizing an anyonic excitation. The Chern--Simons coupling also modifies the screening structure of the gauge fields, producing complex-conjugate masses that yield a common penetration depth with an oscillatory phase. This altered asymptotic behavior breaks the conventional type-I/type-II dichotomy of the Ginzburg--Landau model. As a result, vortex anyons experience short-range repulsion and long-range attraction, enabling the formation of separated multi-vortex bound states with non-monotonic interaction energy.

cond-mat.supr-con↗

arXiv2025

Ultrasound response to time-reversal symmetry breaking below the superconducting phase transition

Ultrasound attenuation is a powerful probe of symmetry-breaking phenomena in superconductors. In this work, we develop a framework to model the ultrasound response of multi-component superconductors undergoing a time-reversal symmetry breaking transition below the superconducting phase transition. By coupling the elastic strain of the crystal lattice to the superconducting order parameters through group-theoretical analysis of tetragonal crystals, we classify how different symmetry channels contribute to the ultrasound signal. Using a two-component Ginzburg--Landau theory, we analyze the temperature dependence of sound velocity across both superconducting and time-reversal symmetry breaking transitions for several cases, including $(A_{1g}, A_{1g})$, $(A_{2g}, B_{1g})$, and $E_g$ representations. Our results demonstrate that ultrasound measurements are highly sensitive to the presence of bilinear Josephson couplings and can distinguish between different realizations of the superconducting state. We further show how external strain can significantly alter the ultrasound response in systems breaking time reversal symmetry.

cond-mat.supr-con↗

arXiv2025

Topological transition from a hopfion to a toron via flexoelectric self-polarization in chiral liquid crystals

The presence of topological defects in apolar chiral liquid crystals cause orientational distortions, leading to non-uniform strain. This non-uniform strain generates an electric polarization response due to the flexoelectric effect, which induces an internal electric field. Associated to this electric field is an electrostatic self-energy, which has a back-reaction on the director field. Calculation of this internal electric field and its resulting back-reaction on the director field is complicated. We propose a method to do such, adapting a method recently developed to study the magnetostatic self-interaction effect on skyrmions in chiral ferromagnets. Bloch skyrmions in chiral magnets are solenoidal and are unaffected by the magnetostatic self-interaction. However, Bloch skyrmions in liquid crystals yield non-solenoidal flexoelectric polarization and, thus, are affected by the electrostatic self-interaction. Additionally, as the flexoelectric coefficients are increased in strength, a transition from a hopfion to a toron is observed in three-dimensional confined systems.

cond-mat.soft↗

arXiv2025

Demagnetization in micromagnetics: magnetostatic self-interactions of bulk chiral magnetic skyrmions

We develop a theoretical and numerical framework for three-dimensional bulk chiral magnets that includes the full magnetostatic dipole-dipole interaction and its back-reaction on the magnetization. Assuming translational invariance along one spatial direction, we analyze the effect of dipolar interactions on three Dzyaloshinskii--Moriya interaction (DMI) terms -- Dresselhaus, Rashba, and Heusler -- corresponding to Bloch, N\'eel, and antiskyrmion textures. In the absence of the dipolar interaction, these three DMI terms are gauge-equivalent and yield degenerate skyrmion energies. Incorporating the non-local dipole-dipole interaction breaks this degeneracy: Bloch skyrmions remain unaffected, N\'eel skyrmions shrink slightly, and Heusler antiskyrmions lose axial symmetry and stabilize into square-lattice crystals. The system is solved using a non-local numerical relaxation method that self-consistently computes the magnetostatic potential from Poisson's equation. Our results show that long-range dipolar interactions can stabilize bulk antiskyrmion crystals in translationally invariant three-dimensional chiral magnets.

cond-mat.mes-hall↗

arXiv2024

Manipulation and trapping of magnetic skyrmions with domain walls in chiral magnetic thin films

In this article we use chiral domain walls to manipulate and trap magnetic skyrmion quasi-particles in chiral magnetic materials such as ultrathin Co/Pt films. The magnetic skyrmions can be orientated such that their interaction with domain walls is repulsive, allowing for them to be stored between domain walls. In certain orientations, the skyrmion can be absorbed into the domain wall, forming a domain wall kink. In other orientations, it can absorbed to form a kink-antikink domain wall with zero topological charge. The magnetic skyrmion can even be orientated in such a way that it remains trapped but creates a topological defect-antidefect pair in one of the walls. By altering the phases of one of the chiral domain walls, one can erase or store the magnetic skyrmion as an isolated soliton or as a domain wall skyrmion/antiskyrmion. This adds a valuable asset to an ever growing toolbox of spintronic nano-devices.

cond-mat.mes-hall↗

arXiv2024

Compressibility of dense nuclear matter in the $\rho$-meson variant of the Skyrme model

We show that coupling the $\textrm{SU}(2)$-valued Skyrme field to the $\rho$-meson solves the long-standing issue of (in)compressibility in the solitonic Skyrme model. Even by including only one $\rho\pi$ interaction term, motivated by a holographic-like reduction of Yang-Mills action by Sutcliffe, reduces the compression modulus from $K_0 \simeq 1080$ MeV, in the massive Skyrme model, to $K_0\simeq 351$ MeV.

hep-th↗

arXiv2024

Skyrmion crystals stabilized by $\omega$-mesons

We investigate the ground state crystalline structure of nuclear matter in the $\omega$-meson variant of the Skyrme model. After minimizing energy with respect to variations of both the Skyrme field and the period lattice, we find four distinct periodic solutions which are similar to those found in the standard Skyrme model. We use these crystals to calculate coefficients in the Bethe--Weizs\"acker semi-empirical mass formula and the compression modulus of infinite nuclear matter, and find a significant improvement as compared with other variants of the Skyrme model.

hep-th↗

arXiv2024

Baby skyrmion crystals stabilized by vector mesons

In this letter we study soliton crystals in the $(2+1)$-dimensional analogue model of the $(3+1)$-dimensional Adkins--Nappi model of nuclear physics. The baby $\omega$-Skyrme model studied here is an $O(3)$ nonlinear $\sigma$ model coupled to a massive vector meson, the $\omega$-meson. Using recently developed methods in the $(3+1)$-dimensional $\omega$-Skyrme model we are able to construct soliton crystals in this $(2+1)$-dimensional baby $\omega$-Skyrme model. The resulting crystals form a hexagonal lattice structure and are qualitatively and quantitatively similar to crystals observed in the standard baby Skyrme model.

hep-th↗

arXiv2023

Generalized skyrmion crystals with applications to neutron stars

In this article we study properties of isospin asymmetric nuclear matter in the generalized Skyrme model. This is achieved by canonically quantizing the isospin collective degrees of freedom of the recently found multi-wall skyrmion crystal. We obtain, for the first time, an equation of state from the Skyrme model which interpolates between infinite isospin asymmetric nuclear matter and finite isospin symmetric atomic nuclei. This enables us to describe neutron stars with crusts within the Skyrme framework. Furthermore, we observe that the symmetry energy tends to a constant value at zero density, which can be identified with the asymmetry coefficient in the semi-empirical mass formula for atomic nuclei. The symmetry energy also reveals a cusp in its structure below the nuclear saturation point $n_0$ at $n_*\sim 3n_0/4$. This cusp density point $n_*$ can be interpreted as the nuclear density whereby the infinite crystalline multi-wall configuration undergoes a phase transition to a finite isolated multi-wall configuration. Both of these observations are observed to be generic features of skyrmion crystals that tend asymptotically to somewhat isolated skyrmion configurations in the zero density limit. We find that the resulting neutron stars from our study agree quite well with recent NICER/LIGO observational data.

hep-th↗

arXiv2023

Skyrme crystals with massive pions

The crystalline structure of nuclear matter is investigated in the standard Skyrme model with massive pions. A semi-analytic method is developed to determine local minima of the static energy functional with respect to variations of both the field and the period lattice of the crystal. Four distinct Skyrme crystals are found. Two of these were already known -- the cubic lattice of half-skyrmions and the $\alpha$-particle crystal -- but two are new. These new solutions have lower energy per baryon number and less symmetry, being periodic with respect to trigonal but not cubic period lattices. Minimal energy crystals are also constructed under the constraint of constant baryon density, and its shown that the two new non-cubic crystals tend to chain and multi-wall solutions at low densities.

hep-th↗

arXiv2022

Baby Skyrmion crystals

This paper describes a model for baby Skyrme crystal chunks with arbitrary potential by considering energy contributions from the bulk and surface of a crystal chunk. We focus on two potentials which yield distinct Skyrme lattices: the standard potential $V=m^2(1-φ^3)$ and the easy plane potential $V=\frac{1}{2}m^2 (φ^1)^2$. In both models, the static energy functional is minimized over all $2$-dimensional period lattices, yielding the minimal energy crystal structure(s). For the standard potential, the Skyrmions form a hexagonal crystal structure, whereas, for the easy plane potential, the minimal energy crystal structure is a square lattice of half-charge lumps. We find that square crystal chunks are the global minima in the easy plane model for charges $B>6$ with $2B$ a perfect square ($m^2=1$). In contrast, we observe that hexagonal crystal chunks in the standard model become the global minima for surprisingly large charges, $B>954$ ($m^2=0.1$).

hep-th↗