Our study of the Shubnikov-de Haas (SdH) effect in highly-oriented pyrolytic graphite (HOPG) systems shows that low-density electrons may occupy a 3D Fermi surface and high-density holes a 2D surface in proton-irradiated HOPG while both carriers occupy a 2D Fermi surface in virgin HOPG. No massless Dirac fermions were evidenced by the SdH oscillations both in virgin HOPG and in proton-irradiated HOPG. Following the examination of the recent controversy on massless Dirac fermions in HOPG, we find that even a small amount of acceptor-like defects may play an important role in the interpretation of SdH oscillations.
- Proton-irradiation in graphite
- Shubnikov-de Haas oscillations
- Spatial separation of charge carriers
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