论文标题
磁性拓扑绝缘子上的相关表面能隙
Facet dependent surface energy gap on magnetic topological insulators
论文作者
论文摘要
磁性拓扑绝缘子（MNBI $ _2 $ te $ _4 $）（bi $ _2 $ _2 $ te $ _3 $）$ _ n $（$ n = 0,1,2,3 $）有望实现外来拓扑状态，例如量子异常霍尔效应（qahe）和轴心隔离器（QAHE）和extrimition $ _________________的$ _2 $ _2 $ _2 $ _2和磁性。但是，在bi $ _2 $ _3 $ _3 $终止的面上是无间隙还是间隙的表面状态，并且很少讨论其在薄膜属性中的后果。在这项工作中，我们发现bi $ _2 $ te $ _3 $终止的面积对于$ n \ ge 1 $化合物是无间隙的。尽管如此，表面bi $ _2 $ te $ _3 $（一层或更多）以及基础的MNBI $ _2 $ _2 $ _4 $ layers综合并引起差距，例如与散装价值频段的杂交间隙重叠，毕竟导致了无处不在的表面。这样的金属表面构成了实现Qahe或ai的根本挑战，这需要至少一个Bi $ _2 $ _2 $ te $ _3 $表面的薄膜中的绝缘差距。从理论上讲，如果两个表面均为MNBI $ _2 $ te $ _4 $层，则在电影中仍然可以实现绝缘阶段。否则，它要求胶片厚度小于10 $ \ sim $ 20 nm，以通过尺寸效果推下散装价带。我们的作品铺平了理解表面状态并设计磁性拓扑材料中的量子设备的方式。
Magnetic topological insulators (MnBi$_2$Te$_4$)(Bi$_2$Te$_3$)$_n$ ($n=0,1,2,3$) are promising to realize exotic topological states such as the quantum anomalous Hall effect (QAHE) and axion insulator (AI), where the Bi$_2$Te$_3$ layer introduces versatility to engineer electronic and magnetic properties. However, whether surface states on the Bi$_2$Te$_3$ terminated facet are gapless or gapped is debated, and its consequences in thin-film properties are rarely discussed. In this work, we find that the Bi$_2$Te$_3$ terminated facets are gapless for $n \ge 1$ compounds by calculations. Despite that the surface Bi$_2$Te$_3$ (one layer or more) and underlying MnBi$_2$Te$_4$ layers hybridize and give rise to a gap, such a hybridization gap overlaps with bulk valence bands, leading to a gapless surface after all. Such a metallic surface poses a fundamental challenge to realize QAHE or AI, which requires an insulating gap in thin films with at least one Bi$_2$Te$_3$ surface. In theory, the insulating phase can still be realized in a film if both surfaces are MnBi$_2$Te$_4$ layers. Otherwise, it requires that the film thickness is less than 10$\sim$20 nm to push down bulk valence bands via the size effect. Our work paves the way to understand surface states and design bulk-insulating quantum devices in magnetic topological materials.
