Wrinkles and Magnetic Flux Trapping in Graphite Nanoflakes: A Possible Source and Manifestation of Room-Temperature Superconductivity

RESUMO

The paper reports on a possible manifestation of local high-temperature superconductivity in graphite nanoflakes obtained from the bulk pyrolytic graphite by an extended grinding and subsequent annealing at 670 K in the air. Analysis of transmission electron microscopy (TEM) images shows that such treatment leads to a formation of high-density wrinkle-type defects at the basal-plane surface. The sample reveals the magnetic flux trapping - one of the key signatures of superconductivity - that persists up to 390 K and above. At the same time, both the as-ground (unannealed) and annealed in the vacuum samples manifest negligible flux trapping, and no wrinkles in their TEM images were found. The direct correlation between the appearance of high-density wrinkle arrays and the detection of the trapped magnetic flux above the room temperature strongly suggests that wrinkled regions serve a source of local high-temperature superconductivity in graphite.