A research group in Japan found a new compound H5S2 that shows a new superconductivity phase on computer simulation. Further theoretical and experimental research based on H5S2 predicted by this group will lead to the clarification of the mechanism behind high-temperature superconductivity, which takes place in hydrogen sulfide.
Last year, a striking news came out that H2S broke the record for superconducting critical temperature under high-pressure. However, the chemical composition ratio of sulfur and hydrogen and the crystal structure during the process in which superconductivity takes place have not been well understood.
A research group led by Takahiro Ishikawa, Specially Appointed Assistant Professor, and Katsuya Shimizu, Professor, at Center for Science and Technology under Extreme Conditions, Graduate School of Engineering Science, Osaka University, Tatsuki Oda, Professor at School of Mathematics and Physics, Kanazawa University, and Naoshi Suzuki, Professor at Faculty of Engineering Science, Kansai University predicted a new superconductivity phase of hydrogen sulfide (H5S2), which was presented at a pressure of 1.1 million bar on computer simulation. The superconducting critical temperature obtained from H5S2, whose calculated value was the same as the experimental value. This result may lead to the clarification of the mechanism behind high-temperature superconductivity, which takes place in hydrogen sulfide by further theoretical and experimental research based on H5S2.
Furthermore, by applying methods used and knowledge obtained by this group to other light element hydrides, it will become possible to establish guidelines for enhancing superconducting critical temperature to near room temperature.
Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (Tc) under high-pressure. The superconducting Tc shows 30–70 K in pressure range of 100–170 GPa (low-Tc phase) and increases to 203 K, which sets a record for the highest Tc in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-Tc phase). Here we present a solid H5S2 phase predicted as the low-Tc phase by the application of the genetic algorithm technique for crystal structure searching and first-principles calculations to sulfur-hydrogen system under high-pressure. The H5S2 phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H2S and H3S molecules. Calculated Tc values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-Tc phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.
SOURCES – Eurekalert, Nature Scientific Reports