Temperature dependence of carrier density in monolayer graphene on SiC

The Hall resistance, which shows a linear magnetic field dependence at low fields, has been widely used to calculate the carrier density n of a two-dimensional system. Nevertheless, it has been pointed out that electron-electron (e-e) interactions enhanced by disorder can result in a logarithmic temperature (lnT) dependence of the Hall slope R_H=1/(ne) without changing the carrier density. Therefore the T dependence of the Hall slope, which may lead to misleading n(T), should be treated with great care. In contrast, Shubnikov-de Haas (SdH) oscillations, which can also be used to calculate n, are not affected by e-e interactions. This is the famous Kohn’s theorem. In this work, we present both Hall and SdH measurements on monolayer graphene grown on SiC. In the low T regime, the minima of the observed SdH oscillations in B do not change with increasing T. Such results clearly demonstrate that n is T-independent over this measurements range. In contrast, the observed a lnT dependence of the Hall slope, which can be ascribed to e-e interactions enhanced by disorder, leads to a wrong interpretation of n(T).