Granular superconductivity at room temperature in bulk highly oriented pyrolytic graphite samples

Abstract

We have studied the magnetic response of two bulk highly oriented pyrolytic graphite (HOPG) samples with different internal microstructure. For the sample with well defined interfaces, parallel to the graphene layers, the temperature and magnetic field hysteresis are similar to those found recently in water-treated graphite powders. The observed behavior indicates the existence of granular superconductivity above room temperature in agreement with previous reports in other graphite samples. The granular superconductivity behavior is observed only for fields normal to the embedded interfaces, whereas no relevant hysteresis in temperature or field is observed for fields applied parallel to them. Increasing the temperature above $\sim 400$ K changes irreversibly the hysteretic response of the sample.

36 pages with 13 figures

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• Invited review: Graphite and its hidden superconductivity
• Nonintrinsic origin of the magnetic-field-induced metal-insulator and electronic phase transitions in graphite
• Influence of surface band bending on a narrow band gap semiconductor: Tunneling atomic force studies of graphite with Bernal and rhombohedral stacking orders
• Collective amplitude mode fluctuations in a flat band superconductor
• Possible superconductivity in multi-layer-graphene by application of a gate voltage
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