DIMENSIONALITY CROSSOVER IN THE TRANSPORT BEHAVIOR OF THE QUASI-ONE-DIMENSIONAL CONDUCTOR H-2(PHTHALOCYANINE)I

Electrical-transport measurements are reported on high-purity H-2(pc)I single crystals and their alloys with Ni(pc)I in the temperature rang e from room temperature to 20 mK and in magnetic fields up to 5.5 T. W e have observed a sharp maximum in conductivity at 1.8 K which we attr ibute to crossover from one- to three-dimensional behavior. The conduc tivity follows a simple quadratic temperature dependence below 1.8 K a nd remains metallic (approximate to 10(4) Omega(-1) cm(-1)) at very lo w temperatures. A negative contribution to the magnetoresistance appea rs at 1.8 K consistent with weak-localization theory.