Journal of Physics and Chemistry of Solids 67, 546 (2006)
Spectroscopies in Novel Superconductors 2004

V. Pantin, J. Avila, M.A. Valbuena, P. Esquinazi, M.E. Dávila and M.C. Asensio

Abstract
A large set of highly oriented graphite (HOPG) samples with different degree of defects has been studied according to their transport properties. The samples showed a dramatic decrease of their conductivity as the degree of defects is increased. For extreme cases, well-ordered HOPG samples displayed a metallic behavior as a function of the temperature, while poorly ordered samples exhibited a reversible semiconductor dependence of their conductivity as a function of temperature changes. Focusing on those samples with either a net metallic or semiconductor behavior, we have carried out a systematic study of their valence band structure by using angle resolved photoemission spectroscopy (ARPES). For those two types of samples, our results reveal an apparent difference of the density of states very close to the Fermi level. Samples with metallic character, show an additional electronic state at the Fermi level, which is quenched, as a higher disorder degree is present.