Scientists Yakov Kopelevich, José Torres, Robson da Silva, Felipe Oliveira, Maria Cristina Diamantini, Carlo Trugenberger, and Valerii Vinokur have reported the first-ever observation of global room-temperature superconductivity in graphite at ambient pressure. The team found that the superconducting critical current is proportional to the inverse of the normal state resistance, indicating a Josephson-junction-like nature of the emerging superconductivity. This discovery could open the way for significant advances in technology. The team’s theoretical model suggests that more room-temperature superconducting materials could be found in stacked materials with linear defects.
Discovery of Room-Temperature Superconductivity in Graphite
A team of researchers, including Yakov Kopelevich, José Torres, Robson da Silva, Felipe Oliveira, Maria Cristina Diamantini, Carlo Trugenberger, and Valerii Vinokur, have reported the observation of global room-temperature superconductivity in cleaved highly oriented pyrolytic graphite. This discovery is significant as room temperature superconductivity under normal conditions has been a major challenge in physics and material science since its discovery.
The Experiment and Findings
The team performed multiterminal measurements at 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. The results revealed that the superconducting critical current Ic(T, B) is governed by the normal state resistance RN(T, B) so that Ic(T, B) is proportional to 1/RN(T, B).
The researchers used a scotch-taped cleaved pyrolytic graphite carrying wrinkles that resulted from the cleaving process. The surface carries bundles of narrow-separated wrinkles, with each bundle separated from each other by a distance of 0.2 mm.
Theoretical Implications
The team developed a theory of global superconductivity emerging in the array of linear structural defects. The theory well describes the experimental findings and demonstrates 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.
Comparison with Previous Research
The discovery of high-temperature superconductivity (HTSC) in the Ba─La─Cu─O cuprates with Tc ≈ 30 K and Y─Ba─Cu─O with Tc being as high as 93 K marked a breakthrough in the RTSC search. However, graphite is yet another promising material taking part in a race for the RTSC. Various experimental groups have also reported localized superconductivity in graphite at temperatures as high as 300 K.
Future Implications
The ideas and concepts explored in this work are not confined to graphite. The theoretical model developed by the team is quite general and guides where to look for more room-temperature superconducting materials. The basic principle uncovered is that linear defects in stacked materials host strong strain gradient fluctuations, which induce the local pairing of electrons into condensate droplets that form JJA-like structures in the planes. The global superconductivity is then established by the effect of the tunneling links connecting the superconducting droplets. If the droplets are sufficiently small, one foresees a fairly high critical superconducting temperature.
