Record-setting superconductor characterized

In late 2014 the condensed-matter community was abuzz with news that Mikhail Eremets and his colleagues at the Max Planck Institute for Chemistry in Germany had discovered that hydrogen sulfide superconducts at 190 K when squeezed to a pressure of 150 GPa. Not only did the superconducting temperature shatter the previous record by 30 K, it’s nearly 10 K higher than the coldest temperature ever measured on Earth’s surface. Intriguingly, the record-breaking superconductor is of the conventional variety described by the venerable Bardeen-Cooper-Schrieffer theory, in contrast to cuprate and iron-based superconductors, whose superconducting mechanism continues to elude researchers. Eremets and his colleagues, aware that H₂S likely couldn’t withstand the high pressures used in their experiments, suspected that their superconductor was a different hydride left from the dissociation of H₂S. Independently, Tian Cui and his team at Jilin University in China had suggested that H₃S should harbor superconductivity around 200 K at 200 GPa. Now Eremets’s group has teamed up with Katsuya Shimizu and colleagues at Osaka University to perform simultaneous resistance and x-ray diffraction measurements that confirm the theorists’ predictions. As shown in the figure, the diffraction pattern, measured at Japan’s SPring-8 synchrotron facility, contains the signatures of H₃S (orange) and elemental sulfur (green), the other dissociation product. The inset shows the H₃S crystal structure (yellow sulfur and blue hydrogen), which was also predicted by theory. The results raise hopes that theory can guide future searches for new high-temperature superconductors. (M. Einaga et al., Nat. Phys., in press, doi:10.1038/nphys3760 .)