Room-temperature superconductivity in carbons – a mini review

Abstract

The search for room-temperature superconductivity in carbons is gathering momentum because it has a long history, impressive track record, clear advancement route, and theoretical backup. The report of a suspected Josephson current in Al-C-Al sandwiches at room temperature, published in Nature 50 years ago, led to the report of a voltage in nano-graphite films believed to mark the reverse Josephson effect. The report on oxygen-doped diamonds led to full-blown superconductivity in boron-doped diamonds. The reports on highly oriented pyrolytic graphite (HOPG) and water-treated graphite powder led to the claim of a current running by itself for 50 days in a ring of HOPG soaked with alkane at room temperature. It also led to a claim of a current running for 1,000 seconds in a ring of graphene soaked in hexane. The carbons are amicable to intercalation chemistry, electrostatic carrier doping, and surface-proving techniques to promote an increase in carrier density, metallization, and applicability of the Ashcroft proposal. Consequently, the high Debye temperatures (1,670, 2,230 and 2,500 K in graphene, diamond and HOPG) may be sufficient to underwrite superconductivity at T∼300 K in carbons, provided the phonon-exchange factor, λ, is around 3 to mark strong enough interactions between electrons and phonons.