Possible Superconductivity at 190 Kelvin in Compressed Sulfur-Hydride
Mikhail Eremets, A. Troyan and A.P. Drozdov, researchers from the Max Planck Institute for Chemistry in Mainz, Germany, say they have measured sulfur hydride superconducting at a temperature of 190 Kelvin (-83 degrees Celsius) at pressures greater than 150 gigapascals.
Sulfur hydride is a "conventional" superconductor described by the BCS theory. The BCS theory was proposed in 1957 by John Bardeen, Leon Cooper and John Schrieffer to explain conventional superconductivity. It asserts that when certain metals are cooled to low temperature, the coherent movement of electrons (Cooper pairs) is facilitated via vibrations called phonons. A phonon and a Cooper pair travel together through a crystal lattice with little or no resistance.
Previously the highest observed transition temperature for a conventional superconductor was 39 K in magnesium-diboride.
Eremet and his team placed sulfur hydride into a diamond anvil cell fitted with electrodes capable of measuring electrical conductivity. They then varied the pressure and temperature inside the cell to see how the resistance changed.
What they found was that, at a pressure of 150 gigapascals, the critical temperature rose to 190 Kelvin. They measured an electrical conductivity change of several orders of magnitude. “We found superconductivity with Tc≈190 K in a H2S sample pressurized to P>150 GPa at T>220 K,” they report
“We proved occurrence of superconductivity by the drop of the resistivity at least 50 times lower than the copper resistivity."
A demonstration of the Meissner effect to confirm the presence of superconductivity has not yet been performed.
(arXiv, et al 12/09/14)