  We report on the conductance from two-contact carrier injection in C60 single
crystals. In the nonlinear regime, the current and voltage obey a power law, I
\~ V^m, where m can be as high as 10 at room temperature. This nonlinear
behavior - the resistance decreases by 6 orders of magnitude without saturation
- is among the highest reported for organic systems, and can be explained by
injection of free carriers into the trap-filling region. We find that H2
annealing suppresses shallow traps and enhances nonlinearity. Two limiting
types of temperature dependence of the nonlinear resistance are observed -
decreasing and increasing resistance at the orientational ordering temperature.
A simple model incorporating deep traps is presented to understand this
behavior and the impact of this model on possible field-effect transistor
action is discussed.

Materials Science