  We investigate the quantum transport properties of surface electrons on a
topological insulator Bi2Te3 nanowire in a magnetotransport study. Although the
nanowires are synthesized by using a relatively coarse method of
electrochemical deposition, clear Aharonov-Bohm oscillations of phases 0 and pi
are observed, owing to the highly coherent surface electron channel. The
oscillation amplitude exhibits exponential temperature dependence, suggesting
that the phase coherence length L_phi is inversely proportional to the
temperature, as in quasi-ballistic systems. In addition, a weak
antilocalization analysis on the surface channel by using a one-dimensional
localization theory, enabled by successful extraction of the surface
contribution from the magnetoconductance data, is provided in support of the
temperature dependence of L_phi.
