Global Room-Temperature Superconductivity in Graphite

Room temperature superconductivity under normal conditions has been a major challenge of physics and material science since its discovery. Here the global room-temperature superconductivity observed in cleaved highly oriented pyrolytic graphite carrying dense arrays of nearly parallel surface line defects is reported. The multiterminal measurements performed at the ambient pressure in the temperature interval 4.5 K <= T <= 300 K and at magnetic fields 0 <= B <= 9 T applied perpendicular to the basal graphitic planes reveal that the superconducting critical current I-c(T, B) is governed by the normal state resistance R-N(T, B) so that I-c(T, B) is proportional to 1/R-N(T, B). Magnetization M(T, B) measurements of superconducting screening and hysteresis loops together with the critical current oscillations with temperature that are characteristic for superconductor-ferromagnet-superconductor Josephson chains, provide strong support for the occurrence of superconductivity at T > 300 K. A theory of global superconductivity emerging in the array of linear structural defects is developed which well describes the experimental findings and demonstrate that global superconductivity arises as a global phase coherence of superconducting granules in linear defects promoted by the stabilizing effect of underlying Bernal graphite via tunneling coupling to the three dimensional (3D) material.