▎ 摘　　要

The quantum Hall (QH) effect in two-dimensional electron and hole gas is studied in high quality graphene samples. Graphene samples whose lateral size similar to 10 mu m were fabricated into mesoscopic devices for electrical transport measurement in magnetic fields. In an intermediate field range of up to 10 T, a distinctive half-integer QH effect is discovered with QH plateaus appearing at a filling factor sequence, v = 4(n + 1/2), where n is the Landau level (LL) index. As the magnetic field increases to the extreme quantum limit, we observe additional QH plateaus at filling factors v = 0, +/- 1, +/- 4. Further detailed investigations show that the presence of the v = 0, +/- 1 QH states indicates the n = 0 LL at the charge neutral Dirac point splits into four sublevels. This lifts both the sublattice and the spin degeneracy, while the QH states at v = +/- 4 can be attributed to lifting of the spin degeneracy of me LLs. Above 30 T of magnetic field, the large quasiparticle gaps between the n = 0 and n = +/- 1 LLs lead to the QH effect that can be observed even at room temperature. (c) 2007 Elsevier Ltd. All rights reserved.