High resolution magnetoresistance data in highly oriented pyrolytic graphite thin samples manifest non-homogenous superconductivity with critical temperature Tc∼25K. These data exhibit: i) hysteretic loops of resistance versus magnetic field similar to Josephson-coupled grains, ii) quantum Andreev's resonances and iii) absence of the Schubnikov-de Haas oscillations. The results indicate that graphite is a system with non-percolative superconducting domains immersed in a semiconducting-like matrix. As possible origin of the superconductivity in graphite we discuss interior-gap superconductivity when two very different electronic masses are present.
@article{arxiv.0711.3542,
title = {Intrinsic Superconductivity at 25 K in Highly Oriented Pyrolytic Graphite},
author = {P. Esquinazi and N. García and J. Barzola-Quiquia and J. C. González and M. Muñoz and P. Rödiger and K. Schindler and J. -L. Yao and M. Ziese},
journal= {arXiv preprint arXiv:0711.3542},
year = {2009}
}