▎ 摘　　要

Charge carriers in a graphene sheet, a single layer of graphite, exhibit distinct characteristics from those in other two-dimensional electronic systems because of their chiral nature. In this paper, we focus on the observation of weak localization in a graphene sheet exfoliated from a piece of natural graphite and nanopatterned into a Hall-bar geometry. Much stronger chiral-symmetry-breaking elastic intervalley scattering in our graphene sheet restores the conventional weak localization. The resulting carrier density and temperature dependence of the phase coherence length reveal that the electron-electron interaction including a direct Coulomb interaction is the main inelastic-scattering factor while electron-hole puddles enhance the inelastic scattering near the Dirac point.