  We report the systematic studies of spin current transport and relaxation
mechanism in highly doped organic polymer film. In this study, we have
determined spin diffusion length (SDL), spin lifetime, and spin diffusion
constant by using different experimental techniques. The spin lifetime
estimated from the electron paramagnetic resonance experiment is much shorter
than the previous expectation beyond the experimental ambiguity. This suggests
that significantly large spin diffusion constant, which is reasonably explained
by the hopping transport mechanism in degenerate semiconductors, exists in
highly doped organic semiconductors. The calculated SDL using the spin lifetime
and spin diffusion constant estimated from our experiment is comparable to the
experimentally obtained SDL of the order of one hundred nanometers. Moreover,
the present study revealed that the spin angular momentum is almost preserved
in the hopping events. In other words, the spin relaxation mainly occurs due to
the spin-orbit coupling at the nanoscale crystalline grains.
