  We report the low temperature current-voltage (I-V) characteristics studies
in quasi-one dimensional conducting polymer nanofibers. We find a threshold
voltage Vt below which little current flows at temperatures below 30-40 K. For
V > Vt current scales as (V/Vt - 1)^zeta, where zeta ~ 1.8-2.1 at high biases.
Differential conductance oscillations are found whose magnitude increases as
temperature decreases below 10 K. We attribute the observed low temperature I-V
behavior to Coulomb blockade effects with a crossover to Luttinger liquid-like
behavior at high temperature. We demonstrate that at low temperatures such a
doped conjugated polymer fiber can be considered as an array of small
conducting regions separated by nanoscale barriers, where the Coulomb blockade
tunneling is the dominant transport mechanism.
