The Heisenberg model for S=1/2 describes the interacting spins of electrons localized on lattice sites due to strong repulsion. It is the simplest strong-coupling model in condensed matter physics with wide-spread applications. Its relevance has been boosted further by the discovery of curate high-temperature superconductors. In leading order, their undoped parent compounds realize the Heisenberg model on square-lattices. Much is known about the model, but mostly at small wave vectors, i.e., for long-range processes, where the physics is governed by spin waves (magnons), the Goldstone bosons of the long-range ordered antiferromagnetic phase. Much less, however, is known for short-range processes, i.e., at large wave vectors. Yet these processes are decisive for understanding high-temperature superconductivity. Recent reports suggest that one has to resort to qualitatively different fractional excitations, spinons. By contrast, we present a comprehensive picture in terms of dressed magnons with strong mutual attraction on short length scales. The resulting spectral signatures agree strikingly with experimental data
Thermodynamically stable skyrmion lattice in tetragonal frustrated antiferromagnet with dipolar interaction
受最近关于GdRu $_2$ Si $_2$的实验结果的启发[Khanh，N.D.，Nakajima，T.，Yu，X.例如，\emph{Nat. Nanotechnol.} \textbf{15}，444-449（2020）]，其中观察到纳米正方形skyrmion晶格，我们提出了在外部磁场中具有偶极相互作用的中心对称四重阻挫反铁磁体的相图的高温部分的简单分析平均场描述。在倒易空间中，偶极力提供动量依赖的双轴各向异性。结果表明，在四元晶格中，对于$ab$平面上相互垂直的调制矢量，在布里渊区的大部分区域内，这种各向异性具有相互垂直的易磁化轴和共线的中间磁化轴，这导致双Q调制自旋结构的稳定化.后者原来是一个正方形的skyrmion晶格在其稳定区域的大部分与拓扑电荷$\pm 1$每个磁性单元格，这是由受抑的交换耦合，因此，纳米尺寸。当存在额外的单离子易轴各向异性时，易轴和中间轴可以互换，从而导致不同的相图。有人认为，后一种情况是相关的GdRu $_2$ Si $_2$。
Meron-mediated phase transitions in quasi-two-dimensional chiral magnets with easy-plane anisotropy: successive transformation of the hexagonal skyrmion lattice into the square lattice and into the tilted FM state
