There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
<p class="first" id="d14656501e95">A superconductor is a material that can conduct
electricity without resistance below
a superconducting transition temperature, Tc. The highest Tc that has been achieved
to date is in the copper oxide system: 133 kelvin at ambient pressure and 164 kelvin
at high pressures. As the nature of superconductivity in these materials is still
not fully understood (they are not conventional superconductors), the prospects for
achieving still higher transition temperatures by this route are not clear. In contrast,
the Bardeen-Cooper-Schrieffer theory of conventional superconductivity gives a guide
for achieving high Tc with no theoretical upper bound--all that is needed is a favourable
combination of high-frequency phonons, strong electron-phonon coupling, and a high
density of states. These conditions can in principle be fulfilled for metallic hydrogen
and covalent compounds dominated by hydrogen, as hydrogen atoms provide the necessary
high-frequency phonon modes as well as the strong electron-phonon coupling. Numerous
calculations support this idea and have predicted transition temperatures in the range
50-235 kelvin for many hydrides, but only a moderate Tc of 17 kelvin has been observed
experimentally. Here we investigate sulfur hydride, where a Tc of 80 kelvin has been
predicted. We find that this system transforms to a metal at a pressure of approximately
90 gigapascals. On cooling, we see signatures of superconductivity: a sharp drop of
the resistivity to zero and a decrease of the transition temperature with magnetic
field, with magnetic susceptibility measurements confirming a Tc of 203 kelvin. Moreover,
a pronounced isotope shift of Tc in sulfur deuteride is suggestive of an electron-phonon
mechanism of superconductivity that is consistent with the Bardeen-Cooper-Schrieffer
scenario. We argue that the phase responsible for high-Tc superconductivity in this
system is likely to be H3S, formed from H2S by decomposition under pressure. These
findings raise hope for the prospects for achieving room-temperature superconductivity
in other hydrogen-based materials.
</p>