Evidence for Disorder Induced Delocalization in Graphite

TL;DR

This study provides evidence that disorder can induce delocalization in graphite, challenging traditional band theory, supported by transport measurements and Raman spectroscopy showing reduced disorder in exfoliated samples.

Contribution

It offers experimental support for a disorder-induced delocalization model in graphite, contrasting with expectations from simple band theory.

Findings

Exfoliated graphite shows high c-axis resistivity and non-monotonic temperature dependence.

Raman spectroscopy indicates reduced disorder in exfoliated samples.

Transport data aligns with the disorder-induced delocalization model.

Abstract

We present electrical transport measurements in natural graphite and highly ordered pyrolytic graphite (HOPG), comparing macroscopic samples with exfoliated, nanofabricated specimens of nanometer thickness. The latter 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 our transport data. Furthermore, 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.