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Cryogenic applications of carbon (C) allotropes such as graphene, highly oriented pyrolytic graphite (HOPG), carbon fibers (CFs), and diamond-like carbon films (DLC) range from CF-enforced high critical temperature superconducting (HTS) wires and tapes for superconducting generators and magnets for fusion reactors, space technology, levitation, or the handling of liquefied gases in cryocoolers. C-based materials combine lightness with excellent thermal, electrical, and mechanical (strength) properties. Proximity-induced superconductivity and engineered ferromagnetism in C allotropes find applications to hetero-structures for enhanced flux pinning or spintronics. Therefore, knowledge of C allotropes' properties is important for their choice of applications.
Herein we present results on magneto-transport properties of CFs, carbon nanotubes, HOPG, as well as amorphous C and DLCs. With the sample in the four-wire arrangement, magneto-resistance data at cryogenic temperatures from 1.9 K or 5 K to 300 K was obtained using the Quantum Design Physical Properties Measurement System. Ion implantation and intercalation produced noticeable changes on the electrical properties, such as electrical resistivity and current carrying capacity. We have found temperature or/and magnetic-field driven insulator-metal-insulator transitions of quantum nature. Just like Bi, graphite has Bose metallic states in which both superconducting and excitonic correlations play a role. The latter become evident in the case of CFs, where both superconducting fluctuations and antiferromagnetic correlations become important at low temperatures. The two-band conduction in HOPG has a thermal activation term explained by others as due to the existence of narrow superconducting channels in which thermal fluctuations can cause phase slips. In addition, observation of giant magnetoresistance suggests the magnetocaloric effect.
Acknowledgements: The Air Force Office of Scientific Research (AFOSR), The Aerospace Systems Directorate (AFRL/RQ), and United Energy Systems (UES, Inc.)