Lu Yu-Shan, Li Jian-Lin, Wu Chien-Te
Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan.
Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan.
Phys Rev Lett. 2021 Nov 19;127(21):217202. doi: 10.1103/PhysRevLett.127.217202.
The study of the magnonic thermal Hall effect in magnets with Dzyaloshinskii-Moriya interaction (DMI) has recently drawn attention because of the underlying topology. Topological phase transitions may arise when there exist two or more distinct topological phases, and they are often revealed by a gap-closing phenomenon. In this work, we consider the magnons in honeycomb ferromagnets described by a Heisenberg Hamiltonian containing both an out-of-plane DMI and a Zeeman interaction. We demonstrate that the magnonic system exhibits temperature (or magnetic field) driven topological phase transitions due to magnon-magnon interactions. Specifically, when the temperature increases, the magnonic energy gap at Dirac points closes and reopens at a critical temperature, T_{c}. By showing that the Chern numbers of the magnonic bands are distinct above and below T_{c}, we confirm that the gap-closing phenomenon is indeed a signature for the topological phase transitions. Furthermore, our analysis indicates that the thermal Hall conductivity in the magnonic system exhibits a sign reversal at T_{c}, which can serve as an experimental probe of its topological nature. Our theory predicts that in CrI_{3} such a phenomenon exists and is experimentally accessible.
由于潜在的拓扑结构，最近对具有Dzyaloshinskii-Moriya相互作用（DMI）的磁体中的磁振子热霍尔效应的研究引起了关注。当存在两个或更多不同的拓扑相时，可能会出现拓扑相变，并且它们通常由能隙闭合现象揭示。在这项工作中，我们考虑由包含面外DMI和塞曼相互作用的海森堡哈密顿量描述的蜂窝状铁磁体中的磁振子。我们证明，由于磁振子-磁振子相互作用，磁振子系统表现出温度（或磁场）驱动的拓扑相变。具体而言，当温度升高时，狄拉克点处的磁振子能隙在临界温度(T_{c})处闭合并重新打开。通过表明磁振子能带的陈数在(T_{c})之上和之下是不同的，我们证实能隙闭合现象确实是拓扑相变的一个标志。此外，我们的分析表明，磁振子系统中的热霍尔电导率在(T_{c})处表现出符号反转，这可以作为其拓扑性质的实验探针。我们的理论预测，在(CrI_{3})中存在这样一种现象并且在实验上是可实现的。
