Quantum coherence phenomenon in disordered Bi₂SeTe₂ topological single crystal: effect of annealing

We report a comparative magnetotransport study on pristine and annealed Bi₂SeTe₂ single crystals. The pristine sample shows a metallic trend from 300 to 180 K, and an insulating behavior for T  <  180 K, whereas the annealed sample exhibits an insulating nature in the entire 4.2-300 K temperature range. Magnetoresistance (MR) of pristine and annealed samples reveals contrasting behaviour as a function of temperature (T) and magnetic field (B). At 4.2 K, the pristine sample shows weak antilocalization (WAL) behavior at low fields and transforms to weak localization (WL) behavior (negative MR) for B  >  2.5 T. Further, the quantum MR behaviours seen at low temperature gradually transform to classical B ² dependent upon increasing the temperatures. In contrast, the annealed sample shows a WAL at small field superimposed on a parabolic feature for B  >  ±4 T at low temperatures (T  <  20 K). It shows a linear MR at intermediate temperatures (40 K  <  T  <  100 K) and a parabolic MR at temperatures T  >  100 K. Hall measurements on both samples exhibit a nonlinear behavior at 4.2 K pointing to the existence of two types of carriers with different mobility. The annealed sample also shows a drastic decrease in mobility by one order of magnitude and a reduction in Ioffe-Regel parameter (k _F l) by a factor of ~3. Disorder-induced localization of bulk carriers and its coexistence with localization-immune surface carriers at low T leads to WAL and WL. MR observed in the annealed sample can be attributed to the presence of both quantum-classical contribution and has been analysed using the Hikami-Larkin-Nagaoka (HLN) equation.