Independence of topological surface state and bulk conductance in three-dimensional topological insulators

Shu Cai,Jiangping Hu,Honghong Wang,Yanchuan Li,Liling Sun,Yazhou Zhou,Satya K Kushwaha,Jing Guo,Gongchang Lin,Qi Wu,Aiguo Li,Vladimir A Sidorov,Ke Yang,Robert J Cava,Xiaodong Li

doi:10.1038/s41535-018-0134-z

Abstract

The archetypical 3D topological insulators Bi2Se3, Bi2Te3, and Sb2Te3 commonly exhibit high bulk conductivities, hindering the characterization of the surface state charge transport. The optimally doped topological insulators Bi2Te2Se and Bi2−xSbxTe2S, however, allow for such characterizations to be made. Here we report an experimental comparison of the conductance for the topological surface and bulk states in Bi2Te2Se and Bi1.1Sb0.9Te2S, based on temperature-dependent high-pressure measurements. We find that the surface state conductance at low temperature remains constant in the face of orders of magnitude increase in the bulk state conductance, revealing in a straightforward way that the topological surface states and bulk states are decoupled at low temperatures, consistent with theoretical models, and confirming topological insulators to be an excellent venue for studying charge transport in 2D Dirac electron systems.

Highlights

Topological insulators (TIs) are, theoretically, quantum materials that display a bulk band gap like an ordinary insulator, but a conducting surface state that is topologically protected due to a combination of spin-orbit interactions and time-reversal symmetry.[1,2,3,4,5,6] The topologically non-trivial nature of the spin-helical Dirac fermion surface states in TIs has attracted wide interest in the research community because it results in rich new physics and materials that have potential applications in quantum technology.[7,8]An ideal TI should have topologically-protected metallic surface states (TSS), and an electrically insulating bulk
We address that shortcoming here, finding that the surface state and bulk charge transport in the two TIs are truly independent at low temperatures
High-pressure measurements addressing other issues have been employed in studies on some TIs,[23,24,25,26,27,28] but here we report the high-pressure investigations of insulating BTS and BSTS single crystals that directly address the interdependence of the surface state and bulk state conductances

Summary

Introduction

Topological insulators (TIs) are, theoretically, quantum materials that display a bulk band gap like an ordinary insulator, but a conducting surface state that is topologically protected due to a combination of spin-orbit interactions and time-reversal symmetry.[1,2,3,4,5,6] The topologically non-trivial nature of the spin-helical Dirac fermion surface states in TIs has attracted wide interest in the research community because it results in rich new physics and materials that have potential applications in quantum technology.[7,8]An ideal TI should have topologically-protected metallic surface states (TSS), and an electrically insulating bulk. C Pressure dependence of the relative behaviors of the crossover temperature, T*(P)/T*(0.1 GPa), for the two TIs BTS and BSTS, showing a downward trend with increasing pressure.

Results

Conclusion