Low carrier concentration crystals of the topological insulator Bi2−xSbxTe3−ySey: a magnetotransport study

Abstract

In 3D topological insulators achieving a genuine bulk-insulating state is an important research topic. Recently, the material system (Bi,Sb) _2 (Te,Se) _3 (BSTS) has been proposed as a topological insulator with high resistivity and a low carrier concentration (Ren et al 2011 Phys. Rev. B http://dx.doi.org/10.1103/PhysRevB.84.165311 84 http://dx.doi.org/10.1103/PhysRevB.84.165311 ). Here we present a study to further refine the bulk-insulating properties of BSTS. We have synthesized BSTS single crystals with compositions around x = 0.5 and y = 1.3. Resistance and Hall effect measurements show high resistivity and record low bulk carrier density for the composition Bi $_{1.46}$ Sb $_{0.54}$ Te $_{1.7}$ Se $_{1.3}$ . The analysis of the resistance measured for crystals with different thicknesses within a parallel resistor model shows that the surface contribution to the electrical transport amounts to 97% when the sample thickness is reduced to 1 μ m. The magnetoconductance of exfoliated BSTS nanoflakes shows 2D weak antilocalization with $\alpha \simeq -1$ as expected for transport dominated by topological surface states.

Keywords

• topological insulator
• magnetotransport
• surface states
• weak antilocalization
• 72.20.My
• 73.25.+i