Colossal negative magnetoresistance in dilute fluorinated graphene

Adatoms offer an effective route to modify and engineer the properties of graphene. In this work, we create dilute fluorinated graphene using a clean, controlled and reversible approach. At low carrier densities, the system is strongly localized and exhibits an unexpected, colossal negative magnetoresistance. The zero-field resistance is reduced by a factor of 40 at the highest field of 9 T and shows no sign of saturation. Unusual "staircase" field dependence is observed below 5 K. The magnetoresistance is highly anisotropic. We discuss possible origins, considering quantum interference effects and adatom-induced magnetism in graphene.