  Studies of negative magnetoresistance in novel materials have recently been
in the forefront of spintronic research. Here, we report an experimental
observation of the temperature dependent negative magnetoresistance in Bi2Te3
topological insulator (TI) nanowires at ultralow temperatures (20 mK). We find
a crossover from negative to positive magnetoresistance while increasing
temperature under longitudinal magnetic field. We observe a large negative
magnetoresistance which reaches -22% at 8T. The interplay between negative and
positive magnetoresistance can be understood in terms of the competition
between dephasing and spin-orbit scattering time scales. Based on the
first-principles calculations within a density functional theory framework, we
demonstrate that disorder (substitutional) by Ga+ ion milling process, which is
used to fabricate nanowires, induces local magnetic moments in Bi2Te3 crystal
that can lead to spin-dependent scattering of surface and bulk electrons. These
experimental findings show a significant advance in the nanoscale spintronics
applications based on longitudinal magnetoresistance in TIs. Our experimental
results of large negative longitudinal magnetoresistance in 3D TIs further
indicate that axial anomaly is a universal phenomenon in generic 3D metals.
