We study the topological phase transitions induced by Coulomb engineering in three triangular-lattice Hubbard models $AB_2$, $AC_3$ and $B_2C_3$, each of which consists of two types of magnetic atoms with opposite magnetic moments. The energy bands are calculated using the Schwinger boson method. We find that a topological phase transition can be triggered by the second-order (three-site) virtual processes between the two types of magnetic atoms, the strengths of which are controlled by the on-site Coulomb interaction $U$. This new class of topological phase transitions have been rarely studied and may be realized in a variety of real magnetic materials.
Topological Magnetoelectric Switching on the Atomic Scale
MnBi 2 Te 4系列的内禀磁性拓扑绝缘体有望实现轴子绝缘体，轴子绝缘体是一种理论上预测的能够相互转换电信号和磁信号的物质状态，其性质令人想起宇宙学的轴子暗物质。在这里，我们报告的第一个实验实现的室温轴子单自旋开关的拓扑超材料MnBi2Te3。在扫描隧道显微镜（STM）实验中，通过使用STM针尖去除MnBi2Te4表面的Te原子层，原位产生了超材料。室温STM研究MnBi2Te3揭示了原子尺度的变化交换间隙和形成纳米级自旋气泡钉扎在亚表面缺陷。我们发现，利用STM针尖的局部电场，MnBi_2Te_3中的单个自旋态可以被可逆地转换，其磁电响应与理论预测的轴子绝缘体的响应相当。所观察到的拓扑表面磁性显着高于体Néel温度。
Construction of topological quantum magnets from atomic spins on surfaces
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）；Department of Applied Physics, Aalto University（阿尔托大学应用物理系）
