Indication of novel magnetoresistance mechanism in (Bi,Sb)$_2$(Te,Se)$_3$ 3D topological insulator thin films

TL;DR

This study reveals an unexpected magnetoresistance behavior in 3D topological insulator thin films, suggesting a new mechanism involving a Zeeman field-induced gap opening that affects electron transport.

Contribution

It introduces a novel magnetoresistance mechanism in (Bi,Sb)$_2$(Te,Se)$_3$ topological insulator films, supported by experimental evidence and a two-liquid transport model.

Findings

Anomalously high weak antilocalization amplitude observed.

Nonlinear Hall effect in weak magnetic fields detected.

Two-liquid model explains transport features with a Zeeman-induced gap.

Abstract

Electron states with the spin-momentum-locked Dirac dispersion at the surface of a three-dimensional (3D) topological insulator are known to lead to weak antilocalization (WAL), i.e. low temperature and low-magnetic field quantum interference-induced positive magnetoresistance (MR). In this work we report on the MR measurements in (Bi,Sb)$_2$(Te,Se)$_3$ 3D topological insulator thin films epitaxially grown on Si(111), demonstrating an anomalous WAL amplitude. This anomalously high amplitude of WAL can not be explained by parabolic or linear MR and indicates the existence of an additional, MR mechanism. Another supporting observation is not linear in the classically weak magnetic field Hall effect in the same films. The increase of the low-field Hall coefficient, with respect to the higher-field value, reaches 10$\%$. We consistently explain both transport features within a two-liquid model, where the mobility of one of the components drops strongly in a weak magnetic field. We argue that this dependence may arise from the Zeeman field induced gap opening mechanism.