Far infrared transmission experiments are performed on ultrathin epitaxial graphite samples in a magnetic field. The observed cyclotron resonancelike 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 $\tilde{c}=1.03\times {10}^6\mathrm{m}/\mathrm{s}$.

• Received 30 May 2006

DOI:https://doi.org/10.1103/PhysRevLett.97.266405