Abstract
Reports of metallic behavior in two-dimensional (2D) systems such as high mobility metal-oxide field effect transistors, insulating oxide interfaces, graphene, and MoS2 have challenged the well-known prediction of Abrahams, et al. that all 2D systems must be insulating. The existence of a metallic state for such a wide range of 2D systems thus reveals a wide gap in our understanding of 2D transport that has become more important as research in 2D systems expands. A key to understanding the 2D metallic state is the metal-insulator transition (MIT). In this report, we explore the nature of a disorder induced MIT in functionalized graphene, a model 2D system. Magneto-transport measurements show that weak-localization overwhelmingly drives the transition, in contradiction to theoretical assumptions that enhanced electron-electron interactions dominate. These results provide the first detailed picture of the nature of the transition from the metallic to insulating states of a 2D system.
Highlights
Previous work has shown that an metal-insulator transition (MIT) does exist for graphene: it is well established that graphene can have a metallic state and Chen, et al have demonstrated that insulating samples result through exposure to ion damage[20]
This report and one by Withers, et al on fluorinated graphene transistors[22] demonstrated R(T) behavior that was consistent with 2-d variable range hopping (VRH)
In 3D materials, it is known that weak-localization (WL) and enhanced electron-electron interactions (EEI) control the metallic transport properties near the MIT
Summary
Several samples of epitaxial graphene were grown via Si sublimation from nominally on-axis SiC (0001) substrates[37]. The characteristic time scales resulting from the fits are shown in the supplementary information While this model appears to provide a good fit to the data, it must be emphasized that the values of the parameters extracted should not be taken too seriously since the theory describes a correction to resistance of a weakly disordered metal, a situation far from that of graphene close to the transition to the strongly localized state that is described here. Magnetoresistance and Hall resistance measurements reveal that WL dominates as the strongly localized state is approached, contrary to the assumptions of renormalization group theories that only treat EEI to describe 2D disordered systems and do not predict a 2D MIT These results are consistent with a scaling model by Dobrosavljevic, et al that predicts an MIT in two dimensions and suggests that a more complete theory is needed for the 2D MIT
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