Magneto-transmission as a probe of Dirac fermions in bulk graphite

Far-infrared magneto-transmission spectroscopy has been used to probe 'relativistic' fermions in highly oriented pyrolytic and natural graphite. Nearly identical transmission spectra of those two materials are obtained, giving the signature of Dirac fermions via absorption lines with an energy that scales as v root B. The Fermi velocity is evaluated to be (c) over tilde = (1.02 +/- 0.02) x 10(6) m s(-1) and the pseudogap at the H point is estimated to |Delta| < 10 meV.