Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics

Abstract

We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system.

Neutron study of in-plane skyrmions in MnSi thin films

“…Bogdanov first identified this Dzyaloshinskii-Moriya (DM) interaction's unusual ability to create stable cylindrical magnetic solitons, known as skyrmions 5,6 , that could potentially form the basis for low-energy magnetic storage devices [7][8][9] . While a chiral interaction is a necessary ingredient to stabilize multi-dimensional solitons in magnetic materials 5,6 and other condensed matter systems [10][11][12] , additional interactions are required to make the skyrmions thermodynamically stable. The importance of various contributions to their stability remains an active area of investigation in both bulk crystals [13][14][15][16] and in nanostructures.…”

Skyrmions in square-lattice antiferromagnets

“…Skyrmions have been the topic of intense research in ferromagnetic materials [1][2][3][4][5][6][7][8][9] as well as numerous other systems [10][11][12][13][14][15]. Skyrmions in ferromagnets have promising characteristics that make them suitable for data storage and transfer: They can be driven by low critical currents [16,17], and they are able to move past pinning sites [18].…”

Synthesizing skyrmion bound pairs in Fe-Gd thin films

“…Fifty years since Skyrme described baryons as topological defects of continuous fields 1 , excited "skyrmion" states have been found in condensed matter systems such as liquid crystals 2 , quantum Hall systems 3 , ferroelectrics 4 , and magnetic materials 5 . Similar excitations were theoretically explored in two-dimensional magnetic systems, which evade ferromagnetic transitions by developing spatially inhomogeneous topological spin defects.…”