Field-doping of C60 crystals: A view form theory

The proposal of using the field-effect for doping organic crystals has raised enormous interest. To assess the feasibility of such an approach, we investigate the effect of a strong electric field on the electronic structure of C60 crystals. Calculating the polarization of the molecules and the splittings of the molecular levels as a function of the external field, we determine up to what field-strengths the electronic structure of C60 stays essentially unchanged, so that one can speak of field-effect doping, in the sense of putting charge carriers into otherwise unchanged states. Beyond these field strengths, the electronic structure changes so much, that on can no longer speak of a doped system. In addition, we address the question of a metal-insulator transition at integer dopings and briefly review proposed mechanisms for explaining an increase of the superconducting transition temperature in field-doped C60 that is intercalated with haloform molecules.