Evidence of surface transport and weak anti-localization in single crystal of Bi2Te2Se topological insulator

TL;DR

This study demonstrates surface-dominated transport and weak anti-localization in high-quality Bi2Te2Se topological insulator crystals, using a novel measurement geometry to isolate surface effects from bulk conduction.

Contribution

The paper introduces a specialized measurement geometry that effectively isolates surface transport in topological insulator crystals, revealing surface conduction and weak anti-localization phenomena.

Findings

Surface transport dominates below 20 K in Bi2Te2Se.

Weak anti-localization observed in magneto-transport measurements.

Bulk resistivity remains high, enabling surface conduction detection.

Abstract

Topological insulators are known to their metallic surface states, a result of strong-spin-orbital coupling, that show unique surface transport phenomenon. But these surface transports are buried in presence of metallic bulk conduction. We synthesized very high quality Bi$_2$Te$_2$Se single crystals by modified Bridgman method, that possess high bulk resistivity of $>$20~$\Omega$cm below 20~K, whereas the bulk is mostly inactive and surface transport dominates. Temperature dependence resistivity follows the activation law like a gap semiconductor in temperature range 20-300~K. We designed a special measurement geometry, which aims to extract the surface transport from the bulk. This special geometry is applied to measure the resistance and found that Bi$_2$Te$_2$Se single crystal exhibits a cross over from bulk to surface conduction at 20~K. Simultaneously, the material also shows strong evidence of weak anti-localization in magneto-transport due to the protection against scattering by conducting surface states. This novel simple geometry is an easy route to find the evidence of surface transport in topological insulators, which are the promising materials for future spintronic applications.