Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 62: Focus Session: High Temperature Superconductivity in Hydrides
TT 62.5: Hauptvortrag
Donnerstag, 10. März 2016, 11:45–12:15, H20
High-pressure phases of S, Se, and P hydrides and their superconducting properties: Predictions from ab-initio theory — •E. K. U. Gross — Max Planck Institute of Microstructure Physics, Halle (Saale), Germany
The quest for novel high-temperature superconductors in the family of hydrogen-rich compounds has recently been crowned with the experimental discovery of a record critical temperature of 190 K in a hydrogen-sulfur compound at 200 GPa. In the present contribution, we investigate the phase diagram of the H-S system, comparing the stability of HnS (n = 1,2,3,4) by means of the minima hopping method for structure prediction. Our extensive crystal structure search confirms the H3S stoichiometry as the most stable configuration at high pressure. Superconducting properties are calculated using the fully ab-initio parameter-free approach of density functional theory for superconductors. We find a Tc of 180 K at 200 GPa, in excellent agreement with experiment. We also show that Se-H has a phase diagram similar to its sulfur counterpart. We predict H3Se to be superconducting at temperatures higher than 120 K at 100 GPa. We furthermore investigate the phase diagram of PHn (n = 1,2,3,4,5,6). The results of our crystal-structure search do not support the existence of thermodynamically stable PHn compounds, which exhibit a tendency for elemental decomposition at high pressure. Although the lowest energy phases of PHn=1,2,3 display Tc values comparable to experiment, it remains uncertain if the measured values of Tc can be fully attributed to a phase-pure compound of PHn.