Terahertz conductivity of topological surface states in Bi1.5Sb0.5Te1.8Se1.2

Abstract

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 Bi1.5Sb0.5Te1.7Se1.3 (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.

Quantum oscillations of the topological surface states in low carrier concentration crystals of Bi2−xSbxTe3Pan1, Никитин2, Wu3 et al. 2016Solid State Communications7100View full textAdd to dashboardCite

“…The composition around (x, y)=(0.50,1.3) was found to be the optimum for bulk insulating behavior, as evidenced by a resistivity of several Ωcm at liquid helium temperatures and a bulk carrier concentration of ∼ 2×10 16 cm −3 . The appealing topological properties of BSTS, notably a tunable Dirac cone, were furthermore demonstrated by ARPES [16], STM and STS [17] and THz Time Domain Spectroscopy [18]. We remark that recently also stoichiometric BiSbTeSe 2 has become an attractive material to investigate topological surface states [19,20,21].…”

High‐Performance THz Emitters Based on Ferromagnetic/Nonmagnetic Heterostructures

“…[4][5][6] The propagation properties of THz waves highly depend on the conductivity of materials following the Drude model, [7] so that many materials such as paper, dry woods, and semiconductor wafers are transparent to the THz waves. [9][10][11] For THz technologies, there is great interest in developing high-performance THz sources. [9][10][11] For THz technologies, there is great interest in developing high-performance THz sources.…”

Terahertz single conductance quantum and topological phase transitions in topological insulator Bi2Se3 ultrathin films

“…However, key physical properties such as transport and electromagnetic properties of TSSs are not readily accessible as the standard electrical and optical measurements yield the total response of TSSs, QWSs and bulk free-carrier states. Indeed, recent terahertz spectroscopic investigations on Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 (BSTS) 16 and Bi 2 Se 3 (ref. 17) reported detection of the contributions from the TSSs, but unambiguously disentangling the individual contributions of constituent entities was so far not feasible due to various problems related to impurities, native defects and surface degradations.…”