Indication for an anomalous magnetoresistance mechanism in (Bi,Sb)2(Te,Se)3 three-dimensional topological insulator thin films

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 ${(\mathrm{Bi},\mathrm{Sb})}_{2}{(\mathrm{Te},\mathrm{Se})}_{3}$ 3D topological insulator thin films epitaxially grown on Si(111), demonstrating an anomalous WAL amplitude. This anomalously high amplitude of WAL cannot 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 strongly drops in a weak magnetic field. We argue that this dependence may arise from the Zeeman-field-induced gap opening mechanism.