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Density functional study of ternary topological insulator thin films

机译：三元拓扑绝缘子薄膜的密度泛函研究

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摘要

Using an ab initio density functional theory based electronic structure method with a semilocal density approximation, we study thin-film electronic properties of two topological insulators based on ternary compounds of Tl (thallium) and Bi (bismuth). We consider TlBiX_2 (X = Se, Te) and Bi_2X-2K (X,Y = Se,Te) compounds which provide better Dirac cones, compared to the model binary compounds Bi_2X_3(X = Se, Te). With this property in combination with a structurally perfect bulk crystal, the latter ternary compound has been found to have improved surface electronic transport in recent experiments. In this article, we discuss the nature of surface states, their locations in the Brillouin zone and their interactions within the bulk region. Our calculations suggest a critical thin film thickness to maintain the Dirac cone which is significantly smaller than that in binary Bi-based compounds. Atomic relaxations or rearrangements are found to affect the Dirac cone in some of these compounds. And with the help of layer-projected surface charge densities, we discuss the penetration depth of the surface states into the bulk region. The electronic spectrum of these ternary compounds agrees very well with the available experimental results.
机译：使用基于从头算密度泛函理论的电子结构方法和半局部密度近似，我们研究了基于Tl（th）和Bi（铋）的三元化合物的两种拓扑绝缘体的薄膜电子性能。我们认为与模型二元化合物Bi_2X_3（X = Se，Te）相比，提供更好狄拉克锥的TlBiX_2（X = Se，Te）和Bi_2X-2K（X，Y = Se，Te）化合物。结合该特性和结构完美的块状晶体，最近的实验发现后一种三元化合物具有改善的表面电子传输。在本文中，我们讨论了表面状态的性质，它们在布里渊区中的位置以及它们在整个区域内的相互作用。我们的计算表明，维持狄拉克锥的临界薄膜厚度要比二元Bi基化合物小得多。发现其中一些化合物的原子弛豫或重排影响狄拉克锥。并借助层投影的表面电荷密度，我们讨论了表面态进入体区的渗透深度。这些三元化合物的电子光谱与可用的实验结果非常吻合。

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