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High-temperature superconductivity remains a focus of experimental and theoretical research. Hydrogen sulfide (H2S) has been reported to be superconducting at high pressures and with a high transition temperature. We report on the direct observation of the expulsion of the magnetic field in H2S compressed to 153 gigapascals. A thin (119)Sn film placed inside the H2S sample was used as a sensor of the magnetic field. The magnetic field on the (119)Sn sensor was monitored by nuclear resonance scattering of synchrotron radiation. Our results demonstrate that an external static magnetic field of about 0.7 tesla is expelled from the volume of (119)Sn foil as a result of the shielding by the H2S sample at temperatures between 4.7 K and approximately 140 K, revealing a superconducting state of H2S., (Copyright © 2016, American Association for the Advancement of Science.)

The metallization of hydrogen directly would require pressure in excess of 400 gigapascals (GPa), out of the reach of present experimental techniques. The dense group IVa hydrides attract considerable attention because hydrogen in these compounds is chemically precompressed and a metallic state is expected to be achievable at experimentally accessible pressures. We report the transformation of insulating molecular silane to a metal at 50 GPa, becoming superconducting at a transition temperature of Tc = 17 kelvin at 96 and 120 GPa. The metallic phase has a hexagonal close-packed structure with a high density of atomic hydrogen, creating a three-dimensional conducting network. These experimental findings support the idea of modeling metallic hydrogen with hydrogen-rich alloy.

Superconductivity in compressed lithium is observed by magnetic susceptibility and electrical resistivity measurements. A superconducting critical temperature (Tc) is found ranging from 9 to 16 kelvin at 23 to 80 gigapascals. The pressure dependence of Tc suggests multiple phase transitions, consistent with theoretical predictions and reported x-ray diffraction results. The observed values for Tc are much lower than those theoretically predicted, indicating that more sophisticated theoretical treatments similar to those proposed for metallic hydrogen may be required to understand superconductivity in dense phases of lithium.

Metals formed from light elements are predicted to exhibit intriguing states of electronic order. Of these materials, those containing boron are of considerable current interest because of their relatively high superconducting temperatures. We have investigated elemental boron to very high pressure using diamond anvil cell electrical conductivity techniques. We find that boron transforms from a nonmetal to a superconductor at about 160 gigapascals (GPa). The critical temperature of the transition increases from 6 kelvin (K) at 175 GPa to 11.2 K at 250 GPa, giving a positive pressure derivative of 0.05 K/GPa. Although the observed metallization pressure is compatible with the predictions of first-principles calculations, superconductivity in boron remains to be explored theoretically. The present results constitute a record pressure for both electrical conductivity studies and investigations of superconductivity in dense matter.

Direct electrical transport measurements in a diamond anvil cell provide evidence for the metallization of cesium iodide (CsI) at a pressure of 115 gigapascals. A drop in the temperature dependence of the resistance was found at pressures above 180 gigapascals, indicating that the CsI was superconductive. The superconductivity changed under the influence of a magnetic field to a lower critical temperature and disappeared above 0.3 tesla. The highest critical temperature at which superconductivity was observed was 2 kelvin, and the critical temperature decreased with increasing pressure.