时间反演对称性破缺驱动的EuB $_6$拓扑相变
Time-reversal symmetry breaking driven topological phase transition in EuB$_6$
摘要：
时间反演对称性（TRS）和能带拓扑之间的相互作用在量子物质的拓扑态中起着至关重要的作用。在时间反演不变系统中，自旋简并带的反宇称反转导致了非平凡的拓扑态，如拓扑绝缘体和狄拉克半金属。当TRS被破坏时，交换场引起带的自旋分裂。一对自旋分裂子带的反转可以产生更多奇异的拓扑态，如量子反常霍尔绝缘体和磁性外尔半金属。到目前为止，这种拓扑相变驱动的TRS打破还没有可视化。利用角分辨光电子能谱，我们证明了当EuB $_6$中形成长程铁磁有序时，TRS破缺导致了布里渊区TRI点处一对自旋分裂子带的带反转.电子结构的剧烈变化导致从TRI普通绝缘体态到TRS断裂拓扑半金属（TSM）态的拓扑相变。值得注意的是，磁性TSM态具有理想的电子结构，其中带交叉位于费米能级，没有任何其他带的干扰。我们的发现不仅揭示了TRS破缺驱动的拓扑相变，而且为探索量子物质磁拓扑态的新物理行为提供了一个很好的平台.
英文摘要：
The interplay between time-reversal symmetry (TRS) and band topology plays a crucial role in topological states of quantum matter. In time-reversal-invariant (TRI) systems, the inversion of spin-degenerate bands with opposite parity leads to nontrivial topological states, such as topological insulators and Dirac semimetals. When the TRS is broken, the exchange field induces spin splitting of the bands. The inversion of a pair of spin-splitting subbands can generate more exotic topological states, such as quantum anomalous Hall insulators and magnetic Weyl semimetals. So far, such topological phase transitions driven by the TRS breaking have not been visualized. In this work, using angle-resolved photoemission spectroscopy, we have demonstrated that the TRS breaking induces a band inversion of a pair of spin-splitting subbands at the TRI points of Brillouin zone in EuB$_6$, when a long-range ferromagnetic order is developed. The dramatic changes in the electronic structure result in a topological phase transition from a TRI ordinary insulator state to a TRS-broken topological semimetal (TSM) state. Remarkably, the magnetic TSM state has an ideal electronic structure, in which the band crossings are located at the Fermi level without any interference from other bands. Our findings not only reveal the topological phase transition driven by the TRS breaking, but also provide an excellent platform to explore novel physical behavior in the magnetic topological states of quantum matter.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
