Owerre S A
Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, Ontario, N2L 2Y5, Canada.
Sci Rep. 2018 Jul 4;8(1):10098. doi: 10.1038/s41598-018-28508-5.
In three-dimensional (3D) quantum magnets, magnonic Weyl points (WPs) featuring linear band crossing of two non-degenerate magnon branches can emerge in certain lattice geometry when time-reversal symmetry is broken macroscopically. Unfortunately, there are very limited 3D quantum magnets that host magnonic WPs, and they are yet to be observed experimentally because the intrinsic perturbative interactions that break time-reversal symmetry macroscopically can be very negligible. Here, we present an alternative means via photo-irradiation, in which magnonic WPs can emerge in 3D quantum magnets without relying on intrinsic perturbative interactions to break time-reversal symmetry. By utilizing the magnonic Floquet-Bloch theory, we put forward the general theory of magnonic Floquet WPs in 3D quantum magnets. We show that periodically driven 3D magnonic Dirac nodal-line (DNL) and 3D magnonic gapped trivial insulators can generate 3D magnonic Floquet WPs, which can be tuned by the incident circularly-polarized light. We demonstrate the existence of magnonic Floquet WPs by combining the study of the magnon dispersions, Berry curvatures, and the anomalous thermal Hall effect. The general theoretical formalism can be applied to different magnetic insulators, and thus extending the concept of magnonic WPs to a broader class of 3D magnetically ordered systems.
在三维（3D）量子磁体中，当时间反演对称性被宏观破坏时，在特定晶格几何结构中会出现具有两个非简并磁振子分支线性能带交叉的磁振子外尔点（WPs）。不幸的是，承载磁振子WPs的三维量子磁体非常有限，并且它们尚未通过实验观测到，因为宏观破坏时间反演对称性的内在微扰相互作用可能非常小。在这里，我们提出一种通过光照射的替代方法，其中磁振子WPs可以在三维量子磁体中出现，而无需依赖内在微扰相互作用来破坏时间反演对称性。通过利用磁振子弗洛凯 - 布洛赫理论，我们提出了三维量子磁体中磁振子弗洛凯WPs的一般理论。我们表明，周期性驱动的三维磁振子狄拉克节线（DNL）和三维磁振子带隙平凡绝缘体可以产生三维磁振子弗洛凯WPs，它们可以通过入射圆偏振光进行调控。我们通过结合对磁振子色散、贝里曲率和反常热霍尔效应的研究，证明了磁振子弗洛凯WPs的存在。这种一般理论形式可以应用于不同的磁绝缘体，从而将磁振子WPs的概念扩展到更广泛的一类三维磁有序系统。
