Evidence for Disorder Induced Delocalization in Graphite

We present electrical transport measurements in natural graphite and highly ordered pyrolytic graphite (HOPG), comparing macroscopic samples with exfoliated, nanofabricated specimen of nanometer thickness. Nano-samples exhibit a very large c-axis resistivity \rho_c - much larger than expected from simple band theory - and non-monotonic temperature dependence, similar to macroscopic HOPG, but in stark contrast to macroscopic natural graphite. A recent model of disorder induced delocalization is consistent with the data. Micro-Raman spectroscopy reveals clearly reduced disorder in exfoliated samples and HOPG, as expected within the model - therefore presenting further evidence for a novel paradigm of electronic transport in graphite.