Magnetic-field dependence of the hole-hole interaction in fluorine-intercalated graphite fibers

Magnetoresistance measurements have been performed in high magnetic fields up to 15 teslas in fluorine-intercalated vapor-deposited graphite fibers with concentrations ${\mathrm{C}}_{4.5}$F and ${\mathrm{C}}_{3.6}$F. Previous studies had shown that the intercalation of fluorine, an acceptor in graphite, induces a two-dimensional hole gas in the graphene layers. The fluorine-intercalation process also introduces disorder into the highly ordered pristine fiber, as exhibited by the transport properties. At high magnetic fields, a positive magnetoresistance is observed and is found to vary strongly with temperature. This phenomenon is explained by the effect of the magnetic field on the hole-hole interaction when the spin subbands are split by the magnetic field. A negative magnetoresistance is observed at low fields, and is explained in terms of weak-localization theory. The magnetoresistance data are fitted with the weak-localization contribution in the weak-field regime, then extrapolated to high fields and this contribution is finally subtracted from the measured values to obtain the hole-hole interaction contribution to the magnetoresistance. From a fit to this latter contribution, a value for the screening parameter is found. The relative importance of the weak localization and hole-hole interaction contributions to the logarithmic increase in ρ(T) at low temperature is discussed.