铋硫族化合物的非对称拓扑态
Unoccupied Topological States on Bismuth Chalcogenides
摘要：
利用角分辨双光子光电子能谱和密度泛函理论研究了拓扑绝缘体Bi $_2$ Te $_{x}$ Se $_{3-x}$（$x=0,2,3$）的能带结构.对于所有的表面线性分散的表面状态被发现在中心的表面布里渊区的能量约1.3 eV以上的费米能级。理论分析表明，这一特征出现在自旋-轨道相互作用诱导的反转局域能隙中。该反演对Bi $_2$ Se、$_3$和Bi $_2$ Te $_2$ Se的电子和结构参数的变化不敏感。在Bi $_2$ Te $_3$中，小的结构变化可以改变局部能隙的特征，这取决于未占据的狄拉克态是否存在。圆二色性测量证实了预期的自旋织构。从这些发现中，我们分配到一个未占用的拓扑表面状态的观察状态。
英文摘要：
The unoccupied part of the band structure of topological insulators Bi$_2$Te$_{x}$Se$_{3-x}$ ($x=0,2,3$) is studied by angle-resolved two-photon photoemission and density functional theory. For all surfaces linearly-dispersing surface states are found at the center of the surface Brillouin zone at energies around 1.3 eV above the Fermi level. Theoretical analysis shows that this feature appears in a spin-orbit-interaction induced and inverted local energy gap. This inversion is insensitive to variation of electronic and structural parameters in Bi$_2$Se$_3$ and Bi$_2$Te$_2$Se. In Bi$_2$Te$_3$ small structural variations can change the character of the local energy gap depending on which an unoccupied Dirac state does or does not exist. Circular dichroism measurements confirm the expected spin texture. From these findings we assign the observed state to an unoccupied topological surface state.
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