磁性斯格明子及其晶格层展弹性现象的物理机理研究

Since the first successful experimental observation of magnetic skyrmions in bulk chiral magnets in 2009, the subject has attracted much interest due to its high mobility to electric current and peculiar topological properties. When exposed to uni-axial tension, the hexagonal lattice of skyrmions in FeGe is found to undergo emergent deformation with a strain of 20% while a uni-axial deformation of merely 0.3% is applied to the underlying thin film. Meanwhile, defects in material not only affect the configuration of skyrmions nearby and lead to appearance of novel emergent particles, but also cause the dynamic “pinning” phenomena of skyrmions. These phenomena indicate existence of profound interaction between magnetic skyrmions and the elastic fields of the underlying material, while little is known about the physical mechanism behind. This project aims at uncovering the physical origin of the emergent elastic property of magnetic skyrmions and their lattice with combined thermodynamic modeling, first principle calculation and Monte Carlo simulation. Moreover, we would like to establish the theoretical methods which quantitatively calculate the emergent elastic coefficients. The project is expanded into two parts, one on the theoretical modeling of the emergent elastic behavior of magnetic skyrmions and their lattice under homogeneous stresses or homogeneous stress gradients; the other on the field configuration calculation of skyrmions or new emergent particles under the effect of localized non-homogeneous stresses cause by defects, and then on the physical mechanism of dynamic pinning phenomena caused by defects on moving skyrmions. The research of this project may help the rising of a new branch in solid state mechanics, called “emergent elasticity”.

自09年首次在手征磁体中被发现以来，磁性斯格明子由于其拓扑手性及优异的电流驱动性质而受到人们的广泛关注。近期发现FeGe薄膜在承受0.3%的单向拉伸应变时，其内部斯格明子晶格出现高达20%的层展应变。同时，材料内部的缺陷不但导致新型层展粒子的出现，而且引起了斯格明子的动力学“钉扎”现象。上述现象说明斯格明子及其晶格与材料内部的弹性场之间存在复杂的耦合，而人们对其中的物理机理了解甚少。本项目致力于发展一套解析推导、数值模拟及实验观测相结合的多尺度系统研究方法，揭示斯格明子及其晶格具备的层展弹性的物理根源，并进一步形成定量分析的模型。项目分两部分展开，一是均匀力场或梯度力场作用下斯格明子及其晶格层展弹性行为的理论模型构建及系数预报。二是含缺陷材料内部非均匀应力场作用下，斯格明子及新型磁性层展粒子场构型预报，及其动力学钉扎现象的机理探索。本项目的开展有望促成“层展弹性力学”这一力学分支的兴起。

自09年首次在手征磁体中被发现以来，磁性斯格明子由于其拓扑手性及优异的电流驱动性质而受到人们的广泛关注。近期发现FeGe薄膜在承受0.3%的单向拉伸应变时，其内部斯格明子晶格出现高达20%的层展应变。同时，材料内部的缺陷不但导致新型层展粒子的出现，而且引起了斯格明子的动力学“钉扎”现象。上述现象说明斯格明子及其晶格与材料内部的弹性场之间存在复杂的耦合，而人们对其中的物理机理了解甚少。本项目致力于发展一套解析推导、数值模拟及实验观测相结合的多尺度系统研究方法，揭示斯格明子及其晶格具备的层展弹性的物理根源，并进一步形成定量分析的模型。项目取得的主要结果分为三部分：一是建立了磁场作用下斯格明子及其晶格层展弹性行为的普适性理论模型，称作“层展弹性理论”，并以此为基础解释了磁场作用下斯格明子晶格的稳定性、变形乃至结构相变等现象；二是建立了力磁耦合场作用下斯格明子及其晶格层展弹性行为的普适性理论模型，称作“交叉层展弹性理论”，并以此为基础解释了大量力磁耦合场作用下斯格明子晶格的稳定、变形、相变等行为；三是在前两部分结果的基础上初步探索了变形斯格明子晶格的动力学行为的变化。本项目的开展有望促成“层展弹性力学”这一力学分支的兴起。