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 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 BiSbTeSe. 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 μm. The magnetoconductance of exfoliated BSTS nanoflakes shows 2D weak antilocalization with as expected for transport dominated by topological surface states.
Highlights
Three dimensional (3D) topological insulators (TIs) have generated intense research interest, because they offer unmatched opportunities for the realization of novel quantum states [2, 3]
We conclude that devices fabricated with submicrometer thickness are sufficiently bulk insulating to exploit the topological surface states by transport techniques
We have presented an extensive study of the bulk-insulating properties of BSTS single crystals
Summary
Three dimensional (3D) topological insulators (TIs) have generated intense research interest, because they offer unmatched opportunities for the realization of novel quantum states [2, 3]. Because of time reversal symmetry and a strong spin–orbit interaction, the surface charge carriers are insensitive to backscattering from non-magnetic impurities and disorder. This makes TIs promising materials for a variety of applications, ranging from spintronics and magnetoelectrics to quantum computation [4,5,6]. The transport properties of the surface states turn out to be notoriously difficult to investigate, due to the dominant contribution from the bulk conduction resulting from intrinsic impurities and crystallographic defects. Potential applications strongly rely on the tunability and robustness of charge and spin transport at the device surface or interface. Achieving surface-dominated transport in the current families of TI materials remains a challenging task, in spite of the progress that has been made recently, including charge carrier doping [13, 14], thin film engineering and electrostatic gating [15, 16]
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