Spontaneous skyrmion ground states in magnetic metals
Spontaneous skyrmion ground states in magnetic metals
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DOI：
10.1038/nature05056
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发表时间：
2006-08-17
期刊：
影响因子：
64.8
通讯作者：
Pfleiderer, C.
中科院分区：
文献类型：
--
作者：
Roessler, U. K.;Bogdanov, A. N.;Pfleiderer, C.
自20世纪50年代以来，海森堡等人一直在研究如何解释连续场中可数粒子的出现(1)。为了寻找基本粒子一般场论的组成部分，人们一直在寻找稳定的局域场构型，但大多数非线性场模型都无法预测它们。作为一个例外，Skyrme成功地将核粒子描述为局域态，即所谓的“skyrmions”(2)。Skyrmions是从微观到宇宙尺度的非线性连续体模型的一个特征（3-6）。在非平衡条件下，或在外场稳定或拓扑缺陷扩散的情况下，发现了skyronic态。例如经典液体中的图灵图案(7)，量子霍尔磁体中的自旋织构(8)，或者液晶中的蓝色相(9)。然而，人们通常认为，skyrmions不能在磁性材料中形成自发的基态，如铁磁序或反铁磁序。在这里，我们从理论上证明了这种假设是错误的，并且在没有外场或缺陷扩散的帮助下，在具有手性相互作用的凝聚态物质系统中，skyrmion织构可能自发形成。我们在基于几个可以通过实验确定的材料特定参数的现象学连续体模型中展示了这一点。我们的模型有一个以前没有考虑过的条件：我们允许磁化强度的软化幅度变化，例如，金属磁铁的特征。我们的模型表明自发的斯基子晶格基态可能普遍存在于大量的材料中，特别是在表面和薄膜中，以及在体化合物中，其中缺乏空间反转对称性导致手性相互作用。
Since the 1950s, Heisenberg and others have addressed the problem of how to explain the appearance of countable particles in continuous fields(1). Stable localized field configurations were searched for an ingredient for a general field theory of elementary particles, but the majority of nonlinear field models were unable to predict them. As an exception, Skyrme succeeded in describing nuclear particles as localized states, so-called 'skyrmions'(2). Skyrmions are a characteristic of nonlinear continuum models ranging from microscopic to cosmological scales(3-6). Skyrmionic states have been found under non-equilibrium conditions, or when stabilized by external fields or the proliferation of topological defects. Examples are Turing patterns in classical liquids(7), spin textures in quantum Hall magnets(8), or the blue phases in liquid crystals(9). However, it has generally been assumed that skyrmions cannot form spontaneous ground states, such as ferromagnetic or antiferromagnetic order, in magnetic materials. Here, we show theoretically that this assumption is wrong and that skyrmion textures may form spontaneously in condensed-matter systems with chiral interactions without the assistance of external fields or the proliferation of defects. We show this within a phenomenological continuum model based on a few material-specific parameters that can be determined experimentally. Our model has a condition not considered before: we allow for softened amplitude variations of the magnetization, characteristic of, for instance, metallic magnets. Our model implies that spontaneous skyrmion lattice ground states may exist generally in a large number of materials, notably at surfaces and in thin films, as well as in bulk compounds, where a lack of space inversion symmetry leads to chiral interactions.