  We report the experimental observation of variable range hopping conduction
in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological
insulator (Bi2Se3). The value of the exponent in the hopping equation was
extracted as ~ 1/2 for different widths of nanowires, which is the proof of the
presence of Efros-Shklovskii hopping transport mechanism in a strongly
disordered system. High localization lengths (0.5nm, 20nm) were calculated for
the devices. A careful analysis of the temperature dependent fluctuations
present in the magnetoresistance curves, using the standard Universal
Conductance Fluctuation theory, indicates the presence of 2D topological
surface states. Also, the surface state contribution to the conductance was
found very close to one conductance quantum. We believe that our experimental
findings shed light on the understanding of quantum transport in disordered
topological insulator based nanostructures.
