METAL-INSULATOR-TRANSITION IN A C-60 - RBC60 AND KC60

At zero pressure polymerized RbC60 is an insulator, whereas polymerize d KC60 is a metal with a slight low-temperature resistive upturn. We r eport measurements of the resistivity of RbC60 under pressure, finding a hysteretic resistive transition in RbC60 near 200 K at 5 kbar, at w hich point the material transforms from insulator to metal. Correcting the resistivity to constant volume, both materials are metallic below the transition with a common low-temperature resistive upturn which i s suppressed under compression.