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arXiv 2209.13629cond-mat.mes-hallcond-mat.str-el
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Half模型的自旋Berry曲率

Spin Berry curvature of the Haldane model

Simon Michel, Michael Potthoff

摘要:

在电子系统中积累的几何Berry相位对经典自由度的慢动力学的反馈由Berry曲率决定。在这里,我们研究当地的磁矩,模拟为经典的自旋,这是本地交换耦合到(自旋)Haldom模型的陈绝缘体。在慢经典自旋动力学的突现运动方程中,存在一个额外的反常几何自旋力矩,它来源于相应的自旋Berry曲率。由于时间反演对称性的显式破缺,这是非零的,但在凝聚态系统中通常很小。我们开发的一般理论和计算的自旋-Berry曲率,主要是在弱交换耦合的限制,在各种参数制度的Halfton模型,特别是接近的拓扑相变和自旋耦合到网站在锯齿形边缘的模型在一个带状几何形状。详细讨论了自旋-Berry曲率张量的空间结构、对称性、非局域元的距离依赖性以及其它性质。对于两个经典自旋的情况,几何自旋力矩的影响导致了反常的非哈密顿自旋动力学。它表明,自旋Berry曲率的大小是决定性的绝缘间隙的大小,系统的大小和本地交换耦合的强度控制。

英文摘要:

The feedback of the geometrical Berry phase, accumulated in an electron system, on the slow dynamics of classical degrees of freedom is governed by the Berry curvature. Here, we study local magnetic moments, modelled as classical spins, which are locally exchange coupled to the (spinful) Haldane model for a Chern insulator. In the emergent equations of motion for the slow classical-spin dynamics there is a an additional anomalous geometrical spin torque, which originates from the corresponding spin-Berry curvature. Due to the explicitly broken time-reversal symmetry, this is nonzero but usually small in a condensed-matter system. We develop the general theory and compute the spin-Berry curvature, mainly in the limit of weak exchange coupling, in various parameter regimes of the Haldane model, particularly close to a topological phase transition and for spins coupled to sites at the zigzag edge of the model in a ribbon geometry. The spatial structure of the spin-Berry curvature tensor, its symmetry properties, the distance dependence of its nonlocal elements and further properties are discussed in detail. For the case of two classical spins, the effect of the geometrical spin torque leads to an anomalous non-Hamiltonian spin dynamics. It is demonstrated that the magnitude of the spin-Berry curvature is decisively controlled by the size of the insulating gap, the system size and the strength of local exchange coupling.

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