Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system

Abstract

A superconductor is a material that can conduct electricity with no resistance below its critical temperature (T c ). The highest T c that has been achieved in cuprates 1 is 133 K at ambient pressure 2 and 164 K at high pressures 3 . As the nature of superconductivity in these materials has still not been explained, the prospects for a higher T c are not clear. In contrast, the BardeenCooper-Schrieffer (BCS) theory gives a guide for achieving high T c and does not put bounds on T c , all that is needed is a favorable combination of high frequency phonons, strong electronphonon coupling, and a high density of states. These conditions can be fulfilled for metallic hydrogen and covalent compounds dominated by hydrogen 4,5 . Numerous calculations support this idea and predict T c of 50-235 K for many hydrides 6 but only moderate T c =17 K has been observed experimentally 7 . Here we studied sulfur hydride 8 where a T c 80 K was predicted 9 . We found that it transforms to a metal at pressure 90 GPa. With cooling superconductivity was found deduced from a sharp drop of the resistivity to zero and a decrease of T c with magnetic field. The pronounce isotope shift of T c in D 2 S is evidence of an electron-phonon mechanism of superconductivity that is consistent with the BCS scenario. The superconductivity has been confirmed by magnetic susceptibility measurements with T c =203 K. The high T c superconductivity most likely is due to H 3 S which is formed from H 2 S under its decomposition under pressure. Even higher T c , room temperature superconductivity, can be expected in other hydrogen-based materials since hydrogen atoms provide the high frequency phonon modes as well as the strong electron-phonon coupling.A search for high, room temperature conventional superconductivity is promising as the BardeenCooperSchrieffer (BCS) theory in the Eliashberg formulation puts no apparent limits on T c .Materials with light elements are especially favorable as they provide high frequencies in the phonon spectrum. Indeed many superconductive materials have been found in this way, but only a moderately high T c =39 K has been found in this search in MgB 2 10 . N. Ashcroft 4 turned attention to hydrogen which has very high vibrational frequencies due to the light hydrogen atom, and provides a strong electron-phonon interaction. Further calculations showed that metallic hydrogen should be a superconductor with a very high critical temperature T c 100-240 K for molecular hydrogen, and T c = 300-350 K in the atomic phase at 500 GPa 11 . However superconductivity in pure hydrogen has not yet been found while the conductive and likely Similar to pure hydrogen, they have high Debye temperatures. Moreover, heavier elements might be beneficial as they contribute to the low frequencies that enhance electron phonon coupling.Importantly, lower pressures are required to metallize hydrides in comparison to pure hydrogen.Ashcroft's general idea was supported in numerous calculations 6,9 predicting high T c`s for many hydrides. So far onl...

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Oxygen‐Rich Lithium Oxide Phases Formed at High Pressure for Potential Lithium–Air Battery Electrode

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