You just can't keep a good superconductor down. An iron-based crystal has been found to regain the ability to conduct electricity without resistance when placed under pressure, breaking the record for the temperature at which superconductivity can survive in the process. But how it does this remains a mystery.
Most superconductors work only at temperatures close to absolute zero. So physicists have been puzzled about why certain materials can superconduct at temperatures approaching 70 kelvin. Liling Sun, a condensed-matter physicist at the Institute of Physics, Chinese Academy of Sciences, in Beijing, and her colleagues have investigated how a relatively new addition to the high-temperature superconducting family, iron selenide, behaves when placed under pressure. "Pressure is a way to tune basic electronic and lattice structures by shortening atomic distances, and it can induce a rich variety of phenomena," says Sun.
Under normal pressure, iron selenide superconducts up to about 30 K, and Sun's team expected that raising the pressure would disrupt this. The researchers squeezed a single crystal of the material, measuring 100 micrometers in diameter and 50 micrometers thick, between two diamond-tipped anvils. At first, they found exactly what they predicted: superconductivity stopped as the pressure approached 10 gigapascals.
But as they increased the pressure above 11.5 GPa the sample began to superconduct again. "Pressure-induced re-emergence of superconductivity has been not found in any families of high-temperature superconductors." says Sun. Furthermore, at pressures of about 12.5 GPa, the sample could superconduct at temperatures up to 48 K -- setting a new record for iron-selenide superconductors. "This really surprised us," says Sun.
More little baby steps towards room temperature superconductivity. To read more, click here.