Sn-doped Bi1.1Sb0.9Te2S bulk crystal topological insulator with excellent properties

Abstract

A long-standing issue in topological insulator research has been to find a bulk single crystal material that provides a high-quality platform for characterizing topological surface states without interference from bulk electronic states. This material would ideally be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, display quantum oscillations from the surface state electrons and be growable as large, high-quality bulk single crystals. Here we show that this material obstacle is overcome by bulk crystals of lightly Sn-doped Bi 1.1 Sb 0.9 Te 2 S grown by the vertical Bridgman method. We characterize Sn-BSTS via angle-resolved photoemission spectroscopy, scanning tunnelling microscopy, transport studies, X-ray diffraction and Raman scattering. We present this material as a high-quality topological insulator that can be reliably grown as bulk single crystals and thus studied by many researchers interested in topological surface states.

Measurement of the topological surface state optical conductance in bulk-insulating Sn-doped Bi1.1Sb0.9Te2S single crystals

“…This extracted Fermi energy is close to, but slightly higher than the 120 meV value for crystals grown by the same method reported in Ref. 19. However, considering the conduction band is found to be 230 meV above the Dirac point, the Fermi level extracted by our study resides inside the band gap, consistent with our transmission measurements.…”

“…The averaged conductances do not scale with thickness and are all close to the value of 0.001 Ω −1 which is reported in Ref. 19. These results further support our point that the conductances we extracted come from topological surface states.…”

“…Moreover, the Dirac point of this compound is below the energy of the maximum of the bulk valence band by 60 meV, making it impossible to study the TSS close to the Dirac point without a contribution from the bulk states. In a recent advance 19 , it has been shown that the material Bi 1.1 Sb 0.9 Te 2 S doped with a very small percentage of Sn results in almost ideally stable, bulk-insulating, highcrystallinity single crystal. This material displays a TSS Dirac point, which is energetically isolated from the bulk bands, extremely low bulk carrier densities and transport that is dominated by the surface states below 100 K 19 .…”

“…In a recent advance 19 , it has been shown that the material Bi 1.1 Sb 0.9 Te 2 S doped with a very small percentage of Sn results in almost ideally stable, bulk-insulating, highcrystallinity single crystal. This material displays a TSS Dirac point, which is energetically isolated from the bulk bands, extremely low bulk carrier densities and transport that is dominated by the surface states below 100 K 19 . In this work, we used time-domain terahertz spectroscopy (TDTS) to study the optical response of this newly discovered bulk-insulating Sn doped TI, Bi 1.1 Sb 0.9 Te 2 S (BSTS).…”

Thermoelectric properties of 3D topological insulator: Direct observation of topological surface and its gap opened states

“…TIs are attracting considerable attention in contemporary materials science showing gapless helical massless Dirac fermions on a two-dimensional (2D) surface or onedimensional (1D) edge [9][10][11] . Although there is no direct relationship, TIs and good TE materials have common features of their properties and actually typical three dimensional TIs (3D-TIs) such as Bi2Se3, Bi2Te3 and Bi2-xSbxTe3 had been studied as a promising candidate for TE materials in the past [12][13][14][15][16][17][18] .…”