A Superconducting Field-Effect Switch

We report on a novel realization of a field-effect device, which allows switching between insulating and superconducting states, the widest possible variation of electrical properties of a material. Because of a low surface state density and the observed superconductivity in alkali metal doped C sub 60, we chose C sub 60 as active material. Thus, we induced three electrons per C sub 60 molecule in the topmost molecular layer of a crystal by field-effect device creating a superconducting switch operating up to 11K. Hence, an insulator is transformed into a superconductor. Moreover, this new technique offers new opportunities to study superconductivity as function of carrier concentration.