Abstract
Recent developments have led to an explosion of activity on skyrmions in three-dimensional (3D) chiral magnets. Experiments have directly probed these topological spin textures, revealed their nontrivial properties, and led to suggestions for novel applications. However, in 3D the skyrmion crystal phase is observed only in a narrow region of the temperature-field phase diagram. We show here, using a general analysis based on symmetry, that skyrmions are much more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit coupling. This enhanced stability arises from the competition between field and easy-plane magnetic anisotropy and results in a nontrivial structure in the topological charge density in the core of the skyrmions. We further show that, in a variety of microscopic models for magnetic exchange, the required easy-plane anisotropy naturally arises from the same spin-orbit coupling that is responsible for the chiral Dzyaloshinskii-Moriya interactions. Our results are of particular interest for 2D materials like thin films, surfaces, and oxide interfaces, where broken surface-inversion symmetry and Rashba spin-orbit coupling naturally lead to chiral exchange and easy-plane compass anisotropy. Our theory gives a clear direction for experimental studies of 2D magnetic materials to stabilize skyrmions over a large range of magnetic fields down to T=0.
Highlights
Skyrmions first arose in the study of hadrons in high energy physics [1], but these topological objects have proved to be central in the study of chiral magnets [2,3,4], in addition to a variety of other condensed matter systems, including the quantum Hall effect [5,6,7] and ultracold atoms [8,9,10]
We show here, using a general analysis based on symmetry, that skyrmions are much more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit coupling
In a variety of microscopic models for magnetic exchange, the required easy-plane anisotropy naturally arises from the same spin-orbit coupling that is responsible for the chiral Dzyaloshinskii-Moriya interactions
Summary
Skyrmions first arose in the study of hadrons in high energy physics [1], but these topological objects have proved to be central in the study of chiral magnets [2,3,4], in addition to a variety of other condensed matter systems, including the quantum Hall effect [5,6,7] and ultracold atoms [8,9,10]. Spin-orbit coupling (SOC) in magnetic systems without inversion gives rise to the chiral Dzyaloshinskii-Moriya (DM) [24,25] interaction Dij · ðSi × SjÞ This competes with the usual Si · Sj exchange to produce spatially modulated states like spirals and SkX. We have proposed [36] that broken surface inversion and Rashba SOC at oxide interfaces necessarily leads to chiral magnetic interactions, leading to phases with spin textures [36,37]. With this motivation, we investigate 2D chiral magnets with broken inversion in the z direction.
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