State Key Laboratory of Surface Physics and Department of Physics, Fudan University, 200433, Shanghai, China.
Department of Physics, University of California Santa Barbara, Santa Barbara, CA, 93106, USA.
Nat Commun. 2019 Oct 8;10(1):4530. doi: 10.1038/s41467-019-12410-3.
A phase transition is often accompanied by the appearance of an order parameter and symmetry breaking. Certain magnetic materials exhibit exotic hidden-order phases, in which the order parameters are not directly accessible to conventional magnetic measurements. Thus, experimental identification and theoretical understanding of a hidden order are difficult. Here we combine neutron scattering and thermodynamic probes to study the newly discovered rare-earth triangular-lattice magnet TmMgGaO. Clear magnetic Bragg peaks at K points are observed in the elastic neutron diffraction measurements. More interesting, however, is the observation of sharp and highly dispersive spin excitations that cannot be explained by a magnetic dipolar order, but instead is the direct consequence of the underlying multipolar order that is "hidden" in the neutron diffraction experiments. We demonstrate that the observed unusual spin correlations and thermodynamics can be accurately described by a transverse field Ising model on the triangular lattice with an intertwined dipolar and ferro-multipolar order.
相变通常伴随着序参量和对称破缺的出现。某些磁性材料表现出奇特的隐藏序相，其中的序参量无法通过常规磁性测量直接探测到。因此，实验识别和理论理解隐藏序相是困难的。在这里，我们结合中子散射和热力学探针研究了新发现的稀土三角晶格磁体 TmMgGaO。弹性中子衍射测量中在 K 点观察到清晰的磁布拉格峰。然而，更有趣的是观察到尖锐且高度弥散的自旋激发，这不能用磁偶极序来解释，而是基态多极序的直接结果，这种多极序在中子衍射实验中“隐藏”起来。我们证明，观察到的异常自旋关联和热力学可以通过三角晶格上的横场伊辛模型准确描述，其中包含交织的偶极和亚铁多极序。
