Weak localization in high quality epitaxial graphene

In this talk, we will present our recent low temperature magneto- transport data obtained in a high quality epitaxial graphene grown on an n-type 6H-SiC(0001) substrate. A Hall bar (50$\mu$m $\times$ 6.25$\mu$m) device was fabricated using the conventional photolithographic technique. The as-grown two- dimensional electron system (2DES) density was $6 \times 10^{11} $ cm$^{-2}$ and mobility 14,000 cm$^2$/Vs. In this device, the so-called half-integer quantum Hall effect states were found at $\nu$ = 2, 6, and 10 in high magnetic fields. Close to $B=0$, a strong weak-localization (WL) peak was observed. We fitted this WL peak based on a well-developed theoretical model and obtained the values of the phase coherence ($L_{\phi}$), intravalley ($L_ {\star}$), and intervalley ($L_{iv}$) scattering lengths. $L_ {\phi}$ first increases with decreasing temperature ($T$), $L_ {\phi} \propto T^{-1/2}$, and then saturates below $T \sim 1$K. $L_{iv}$ and $L_{\star}$ are in the order of half nanometer and in general independent of $T$.