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A spectroscopic study of the superconducting phase in sulfur hydride under extreme pressures is presented, revealing the energy scale for the electron–phonon interaction in this system.

M. I. Eremets, V. S. Minkov, A. P. Drozdov and P. P. Kong discuss the substantial progress made in discovering and developing near-room-temperature superconductivity in hydrogen-rich materials. They focus on achieving reproducibility under the challenging experimental conditions of megabar pressures.

Despite decades of intense theoretical, experimental and computational effort, a microscopic theory of high-temperature superconductivity is not yet established. Eight researchers share their contributions to the search for a better understanding of unconventional superconductivity and their hopes for the future of the field.

Measurements of the trapped magnetic flux in hydrides at high pressure provide further evidence that these materials are superconducting at high temperatures.

Superconductivity in hydrides has been primarily explored by electrical transport measurements. Here, the authors perform SQUID magnetometry under extreme high-pressure and report characteristic superconducting parameters for Im-3m-H₃S and Fm-3m- LaH₁₀—the representative members of two families of high-temperature superconducting hydrides.

The progress in generating high static pressures in diamond anvil cells opens opportunities for studying novel materials with unusual properties. Here, the authors report a universal high-pressure diamond edge Raman scale up to 500 gigapascals, which does not require an additional pressure sensor.

The discovery of superconductivity in metal hydrides requires an understanding of hydrogen interactions with the heavy atom sublattice under high pressure. Here, the authors report evidence of a strong effect of hydrogen on the density increase of 4d yttrium states and strong anharmonic vibrations of yttrium atoms in YH₃.

The discovery of high temperature superconductivity in hydrogen-rich compounds stimulates further extensive studies. Here, the authors report superconductivity in pressurized yttrium-hydrogen system with highest predicted T_c among binary compounds.

Ionization of highly compressed ammonia has previously been predicted by computation. Here, the authors provide experimental evidence for this autoionization process at high pressures, showing the transformation of molecular ammonia into ammonium amide.

Molecular hydrogen is expected to display metallic properties under high pressures, but so far experiments performed at low temperatures ( 100 K) have showed that hydrogen remains insulating up to 300 GPa. A transformation of normal molecular hydrogen to a conductive and metallic state at room temperature is now observed above 220 GPa.

Conventional superconductivity is observed at 203 kelvin in the sulfur hydride system, well above the highest superconducting transition temperature obtained in the copper oxides, raising hopes that even higher transition temperatures will be discovered in other hydrogen-rich systems.

The predicted metallization of hydrogen has long fascinated high-pressure physicists. Conductivity and spectroscopic measurements now reveal that above pressures of 350 GPa, hydrogen starts to conduct in a manner akin to a semimetal.

Superconductivity was recently observed in the binary iron-based compound, FeSe. It is now shown that under pressure, the transition temperature can rise above 36 K. In addition, no static magnetic ordering is observed for this system, contrary to FeAs superconductors.

A lanthanum hydride compound at a pressure of around 170 gigapascals is found to exhibit superconductivity with a critical temperature of 250 kelvin.