ABRUPT DIMENSIONAL CROSSOVER IN THE QUASI-ONE DIMENSION AL CONDUCTOR,H2(PC)I

H2(pc)I is known to have highly anisotropic electronic and structural properties. Electrical conductivity and magnetoresistance measurements have been performed on high purity H2(pc)I single crystals ranging fr om room temperature to 20 mK in magnetic fields up to 5.5 tesla. We ha ve observed abrupt changes in both measurements around 2 K. Conductivi ty follows a simple quadratic temperature dependence below 2 K and rem ains metallic (almost-equal-to 1000 OMEGA-1 cm-1) down to very low tem peratures, 20 mK. This phenomenon has not been reported previously in quasi-one dimensional conductors. We suggest that H2(pc)I experiences an abrupt dimensional crossover from a 1 dimensional regime to a 3 dim ensional one below 2 K.