Planar Hall effect and magnetoresistance of Sb₂Te₃ epitaxial films

The measurements of anisotropic magnetoresistance (AMR), planar Hall effect (PHE) and temperaturedependent conductivity in materials with strong spin-orbit coupling yield valuable information about charge carrier scattering processes, localization effects, and band topology. Although electronic structure calculations establish the sesqui-chalcogenide Sb2Te3 a topological insulator (TI), detailed measurements of AMR and PHE are valuable to address the manifestations of the band topology on charge carrier transport in this system. Here, we report on measurements of the longitudinal and Hall resistivity,.xx and.xy, respectively, of the Sb2Te3 films of varied crystallinity over a wide phase space of temperature (T), magnetic field (B), and the angle between B and charge current density (J). The films exhibit semiconducting or metallic behavior depending on their crystallinity. The epitaxial films on (0001) sapphire grown at 150. C are metallic with a hole carrier density (nh) and mobility (mu h) of similar to 1019 cm-3 and similar to 102 cm2 V-1 s-1, respectively, at room temperature. The conduction in the semiconducting film exhibits a Shklovskii-Efros (SE)-type variable range hopping (VRH) at very low temperature, with a transition to the Mott type VRH at T similar to 30 K. The SE-type VRH is characterized by a Coulomb gap of 0.3 meV and a localization length of similar to 12 nm, which matches with the average crystallite size in these disordered films. While signatures of weak antilocalization are seen in the magnetoresistance (MR) of epitaxial films at T similar to 20 K, the MR at T > 20 K agrees with Kohler's rule when corrected for the temperature variation of carrier density. The epitaxial films are characterized by a negative AMR and PHE which varies quadratically with magnetic field, but the orbital plots of.xy vs.xx negate the presence of a chiral anomaly in transport. The amplitude of MR anisotropy for 100.C grown Sb2Te3 film is similar to 102n similar to m at 300 K, which is an order of magnitude larger than in Bi2Te3 and potentially important for the development of AMR-based sensors.