Negative c-axis magnetoresistance in graphite

We have studied the c-axis interlayer magnetoresistance (ILMR), R-c(B) in graphite. The measurements have been performed on strongly anisotropic highly oriented pyrolytic graphite (HOPG) and single crystalline Kish graphite samples in magnetic field up to B = 9 T, and the temperature interval 2 K <= T <= 300 K. We have observed negative magnetoresistance, dR(c)/dB < 0, for B parallel to c-axis for both samples above a certain field B-m(T) > 5.4 T and 0.2 T for HOPG and Kish graphite, respectively. The results can be understood consistently by assuming that ILMR is related to a tunneling between zero-energy Landau levels of quasi-two-dimensional Dirac fermions, in a close analogy with the behavior reported for alpha-(BEDT-TIT)(2)I-3 [N. Tajima, et al., Phys. Rev. Lett. 102 (2009) 176403], another multilayer Dirac electron system. (C) 2010 Elsevier B.V. All rights reserved.