Weak localization and anti-localization in graphene. (a) The sample is studied for various carrier densities (here I, II and III). The QHE shows that the sample is indeed two-dimensional (see Section 7.4). The sample is annealed at 400 K for 2 hours to increase its homogeneity. (b), (c), and (d) Variation of the magnetoresistance behavior as and are changed. A transition occurs between WL and WAL and negative magnetoconductance (WAL) is observed for low and high due to the competition between valley scattering and dephasing processes (see text). Figure from [116].