Revealing electrically undetectable room temperature surface-mobility of bulky topological insulators by spectroscopic techniques

TL;DR

This study uses spectroscopic techniques to measure the surface mobility of topological insulator Bi2Te3 at room temperature, revealing record-high mobility values despite bulk conduction and phonon effects, supporting persistent topological protection.

Contribution

It demonstrates a spectroscopic method to evaluate room-temperature surface mobility in topological insulators, overcoming limitations of electrical transport measurements.

Findings

Record-high surface mobility exceeding 33,000 cm^2/(Vs) at RT.

Surface topological protection persists at room temperature.

Spectroscopic techniques effectively distinguish surface and bulk states.

Abstract

High surface-mobility, which is attributable to topological protection, is a trademark of three-dimensional topological insulators (3DTIs). Exploiting surface-mobility indicates successful application of topological properties for practical purposes. However, the detection of the surface-mobility has been hindered by the inevitable bulk conduction. Even in the case of high-quality crystals, the bulk state forms the dominant channel of the electrical current. Therefore, with electrical transport measurement, the surface-mobility can be resolved only below-micrometer-thick crystals. The evaluation of the surface-mobility becomes more challenging at higher temperatures, where phonons can play a role. Here, using spectroscopic techniques, we successfully evaluated the surface-mobility of Bi2Te3 (BT) at room temperature (RT). We acquired the effective masses and mean scattering times for both the surface and bulk states using angle-resolved photoemission and terahertz time-domain spectroscopy. We revealed a record-high surface-mobility for BT, exceeding 33,000 cm^2/(Vs) per surface sheet, despite intrinsic limitations by the coexisting bulk state as well as phonons at RT. Our findings partially support the interesting conclusion that the topological protection persists at RT. Our approach could be applicable to other topological materials possessing multiband structures near the Fermi level.