  Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been
investigated at high and low bulk charge carrier concentrations. At low charge
carrier density the WAL curves scale with the normal component of the magnetic
field, demonstrating the dominance of topological surface states in
magnetoconductivity. At high charge carrier density the WAL curves scale with
neither the applied field nor its normal component, implying a mixture of bulk
and surface conduction. WAL due to topological surface states shows no
dependence on the nature (electrons or holes) of the bulk charge carriers. The
observations of an extremely large, non-saturating magnetoresistance, and
ultrahigh mobility in the samples with lower carrier density further support
the presence of surface states. The physical parameters characterizing the WAL
effects are calculated using the Hikami-Larkin-Nagaoka formula. At high charge
carrier concentrations, there is a greater number of conduction channels and a
decrease in the phase coherence length compared to low charge carrier
concentrations. The extremely large magnetoresistance and high mobility of
topological insulators have great technological value and can be exploited in
magneto-electric sensors and memory devices.
