通过表面取向调整拓扑绝缘体的电子织构
Tailoring the electronic texture of a topological insulator via its surface orientation
摘要：
三维拓扑绝缘体晶体由金属表面包围的绝缘体块组成，并且可以获得关于表面态能带拓扑和自旋织构的详细理论预测。虽然目前已知几种拓扑绝缘体材料，但这些金属状态的存在和拓扑结构仅针对给定材料的一个特定表面取向进行过探索。对于大多数拓扑绝缘体，例如Bi $_{1-x}$ Sb $_{x}$和Bi $_2$ Se $_3$，该表面是密排（111）表面，并且它支持一个拓扑保证的表面态狄拉克锥。在这里，我们通过实验实现了一个非密排表面的拓扑绝缘体，Bi $_{1-x}$ Sb $_{x}$（110），和探测的表面态拓扑结构的角分辨光电发射。正如预期的那样，这个表面也支持金属态，但表面取向的变化大大改变了能带拓扑结构，导致三个狄拉克锥，而不是一个，与理论预测非常一致，但与任何其他实验研究的TI表面相反。这说明了通过其晶体学方向来定制表面的基本拓扑性质的可能性。在这里，它引入了一个谷自由度以前没有实现的拓扑绝缘体系统。
英文摘要：
Three dimensional topological insulator crystals consist of an insulating bulk enclosed by metallic surfaces, and detailed theoretical predictions about the surface state band topology and spin texture are available. While several topological insulator materials are currently known, the existence and topology of these metallic states have only ever been probed for one particular surface orientation of a given material. For most topological insulators, such as Bi$_{1-x}$Sb$_{x}$ and Bi$_2$Se$_3$, this surface is the closed-packed (111) surface and it supports one topologically guaranteed surface state Dirac cone. Here we experimentally realise a non closed-packed surface of a topological insulator, Bi$_{1-x}$Sb$_{x}$(110), and probe the surface state topology by angle-resolved photoemission. As expected, this surface also supports metallic states but the change in surface orientation drastically modifies the band topology, leading to three Dirac cones instead of one, in excellent agreement with the theoretical predictions but in contrast to any other experimentally studied TI surface. This illustrates the possibility to tailor the basic topological properties of the surface via its crystallographic direction. Here it introduces a valley degree of freedom not previously achieved for topological insulator systems.
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