Linear positive and negative magnetoresistance in topological insulator Bi₂Se₃ flakes

The linear positive magnetoresistance (MR) and negative MR are emerging as intriguing phenomena in topological materials. Here, we report the magnetotransport properties of topological insulator Bi₂Se₃ flakes with different thicknesses grown by chemical vapor deposition. A non-saturating positive MR is observed in the perpendicular fields (B⊥I), while an evident negative MR is observed in the parallel fields (B//I). Both the positive MR and negative MR show a linear magnetic field dependence at high magnetic fields (B > 8 T). In addition, two types of carriers are extracted from the nonlinear Hall resistance measurements, which are attributed to the Bi₂Se₃ bulk electrons and the electron accumulation layer at the surface or Bi₂Se₃/SiO₂ interface, respectively. The conductivity fluctuations in the accumulation layer are believed to be the origin for the observation of positive MR in the perpendicular fields and negative MR in the parallel fields with linear and non-saturating characteristics.