Perspective: (Beyond) spin transport in insulators
Perspective: (Beyond) spin transport in insulators
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DOI：
10.1063/1.5054123
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发表时间：
2018-11
影响因子：
3.2
通讯作者：
Y. Tserkovnyak
中科院分区：
文献类型：
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作者：
Y. Tserkovnyak
具有动态自旋自由度的绝缘材料最近已经成为自旋流的可行管道。然而，其中包含的传输现象比最初设想的要丰富得多。特别是，集体序参数纹理的拓扑性质可以产生不基于任何特定对称性的守恒定律。因此，出现的连续性关系是强大的结构缺陷和各向异性，这将是有害的传统的自旋电流（依赖于近似的自旋旋转对称性）。因此，基本的通量取代了绝缘体中的自旋流概念，为称为拓扑流体动力学的非平衡现象奠定了基础。在这里，我们概述了我们目前的理解的基本成分，基于能量的电控注入拓扑流通过接口，沿着与一个相互的信号产生的流出的守恒量。我们将重点讨论后者的两个例子：一维系统中的绕组动力学，它取代了轴对称易平面磁体的自旋超流性，以及二维海森堡型磁体中的skyrmion动力学。这些例子将说明拓扑流的基本共同点，并提示在自旋电子系统中生成和检测拓扑流的一般策略。我们也将简要讨论序参数空间的其他维数和类型的推广。
Insulating materials with dynamical spin degrees of freedom have recently emerged as viable conduits for spin flows. Transport phenomena harbored therein are, however, turning out to be much richer than initially envisioned. In particular, the topological properties of the collective order-parameter textures can give rise to conservation laws that are not based on any specific symmetries. The emergent continuity relations are thus robust against structural imperfections and anisotropies, which would be detrimental to the conventional spin currents (that rely on approximate spin-rotational symmetries). The underlying fluxes thus supersede the notion of spin flow in insulators, setting the stage for nonequilibrium phenomena termed topological hydrodynamics. Here, we outline our current understanding of the essential ingredients, based on the energetics of the electrically-controlled injection of topological flows through interfaces, along with a reciprocal signal generation by the outflow of the conserved quantity. We will focus on two examples for the latter: winding dynamics in one-dimensional systems, which supplants spin superfluidity of axially-symmetric easy-plane magnets, and skyrmion dynamics in two-dimensional Heisenberg-type magnets. These examples will illustrate the essential common aspects of topological flows and hint on generic strategies for their generation and detection in spintronic systems. Generalizations to other dimensions and types of order-parameter spaces will also be briefly discussed.