Dirac fermions at the H point of graphite:: Magnetotransmission studies

We report on far infrared magnetotransmission measurements on a thin graphite sample prepared by exfoliation of highly oriented pyrolytic graphite. In a magnetic field, absorption lines exhibiting a blueshift proportional to root B are observed. This is a fingerprint for massless Dirac holes at the H point in bulk graphite. The Fermi velocity is found to be (c) over tilde = (1.02 +/- 0.02) x 10(6) m/s and the pseudogap vertical bar Delta vertical bar at the H point is estimated to be below 10 meV. Although the holes behave to a first approximation as a strictly 2D gas of Dirac fermions, the full 3D band structure has to be taken into account to explain all the observed spectral features.