Disorder driven variations in magnetoresistance and planar Hall effect in Bi2Te3 thin films

Abstract

The degenerately doped sesquichalcogenide Bi2Te3, a well-known thermoelectric material, has attracted much attention in recent years as a topological insulator in which conducting surface states lead to exotic electronic transport. Here we report the observation of anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) in polycrystalline thin films of Bi2Te3 over a broad range of temperature and magnetic field strength. The values of AMR, PHE and the Hall mobility (μH) are compared with results of similar measurements on single crystals and epitaxial films of Bi2Te3, where these properties are understood in the framework of electronic transport in the topologically protected conducting surface states. Our textured polycrystalline films show a robust metallic character with a carrier density (ns) and mobility μH of 9×1020 cm−3 and 16.7 cm2V−1s−1 respectively. This carrier density is higher and the mobility lower by an order of magnitude compared to the reported values of ns and μH in epitaxial films and single crystals. However, we see a comparable AMR and PHE in our films for which the concept of conducting surface states is ill-defined due to their polycrystallinity and disordered structure. We suggest that an anisotropic backscattering of charge carriers in the strongly spin – orbit coupled electronic states of this heavy-metal-based non-magnetic compound may lead to the measured resistivity anisotropy. The observation of AMR and PHE in polycrystalline films may be important for scalable production of Bi2Te3 based AMR and PHE sensors of magnetic fields.