Landau level spectroscopy of ultrathin graphite layers
  Far infrared transmission experiments are performed on ultrathin epitaxial graphite samples in a magnetic field. The observed cyclotron resonance-like and electron-positron-like transitions are in excellent agreement with the expectations of a single-particle model of Dirac fermions in graphene, with an effective velocity of c* = 1.03 x 10^6 m/s. 
M.L. Sadowski, G. Martinez, M. Potemski, C. Berger, W.A. de Heer