Magnon Spin-Momentum Locking: Various Spin Vortices and Dirac magnons in Noncollinear Antiferromagnets
Magnon Spin-Momentum Locking: Various Spin Vortices and Dirac magnons in Noncollinear Antiferromagnets
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DOI：
10.1103/physrevlett.119.107205
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发表时间：
2017-09-08
影响因子：
8.6
通讯作者：
Okuma, Nobuyuki
中科院分区：
文献类型：
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作者：
Okuma, Nobuyuki
本文将自旋动量锁定的概念推广到磁振子系统，导出了一般两体自旋哈密顿量的单磁振子态自旋期望值的计算公式。我们给出了磁振子自旋与动量无关的不通过条件。作为磁振子自旋动量锁定的例子，我们分析了一维Neel序反铁磁体和二维120度结构的kagome晶格反铁磁体。我们发现，即使哈密顿量具有z轴自旋旋转对称性，磁振子的自旋也依赖于它的动量，这可以用奇异带点或U（1）对称性破缺来解释.在kagome晶格反铁磁体中产生的动量空间中的自旋涡旋具有缠绕数Q =-2，而在拓扑绝缘体表面态中观察到的典型自旋涡旋的特征在于Q =+1。在另一个kagome晶格反铁磁体中发现了表面态的磁振子类似物，即Q =+1的Dirac磁振子。我们还通过使用Poincare-Hopf指标定理导出了Q的求和规则。
We generalize the concept of the spin-momentum locking to magnonic systems and derive the formula to calculate the spin expectation value for one-magnon states of general two-body spin Hamiltonians. We give no-go conditions for magnon spin to be independent of momentum. As examples of the magnon spinmomentum locking, we analyze a one-dimensional antiferromagnet with the Neel order and two-dimensional kagome lattice antiferromagnets with the 120 degrees structure. We find that the magnon spin depends on its momentum even when the Hamiltonian has the z-axis spin rotational symmetry, which can be explained in the context of a singular band point or a U(1) symmetry breaking. A spin vortex in momentum space generated in a kagome lattice antiferromagnet has the winding number Q = -2, while the typical one observed in topological insulator surface states is characterized by Q = +1. A magnonic analogue of the surface states, the Dirac magnon with Q = +1, is found in another kagome lattice antiferromagnet. We also derive the sum rule for Q by using the Poincare-Hopf index theorem.