Room-Temperature Voltage Rectification in Graphite

Four-probe current-voltage (I-V) characteristics were measured on 80-250 nm thick graphite samples, obtained by cleaving and placed on Si substrate, in the temperature interval 2 K $\le $ T $\le $ 300 K and applied magnetic field up to 9 T. Nonlinear and/or hysteretic I-V curves with a pronounced asymmetry with respect to the current polarity were obtained even at T = 300 K. We demonstrate that voltage rectification and related effects in graphite resemble very much that known for inhomogeneous superconducting systems [1], suggesting the occurrence of superconducting correlations in graphite at room temperature. We also discuss the role of the ferromagnetic ordering at graphitic edges in the observed phenomena. \\[4pt] [1] G. Carapella and G. Costabile, Phys. Rev. Lett. 87, 077002 (2001).