文章基本信息

标题：Terahertz conductivity of topological surface states in Bi_1.5Sb_0.5Te_1.8Se_1.2
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作者：Chi Sin Tang ; Bin Xia ; Xingquan Zou 等
期刊名称：Scientific Reports
电子版ISSN：2045-2322
出版年度：2013
卷号：3
DOI：10.1038/srep03513
出版社：Springer Nature
摘要：Topological insulators are electronic materials with an insulating bulk and conducting surface. However, due to free carriers in the bulk, the properties of the metallic surface are difficult to detect and characterize in most topological insulator materials. Recently, a new topological insulator Bi_1.5Sb_0.5Te_1.7Se_1.3 (BSTS) was found, showing high bulk resistivities of 1–10 Ω.cm and greater contrast between the bulk and surface resistivities compared to other Bi-based topological insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity of BSTS single crystals, disentangling the surface and bulk contributions. We find that the Drude spectral weight is 1–2 orders of magnitude smaller than in other Bi-based topological insulators, and similar to that of Bi₂Se₃ thin films, suggesting a significant contribution of the topological surface states to the conductivity of the BSTS sample. Moreover, an impurity band is present about 30 meV below the Fermi level, and the surface and bulk carrier densities agree with those obtained from transport data. Furthermore, from the surface Drude contribution, we obtain a ~98% transmission through one surface layer — this is consistent with the transmission through single-layer or bilayer graphene, which shares a common Dirac-cone feature in the band structure.