High temperature superconductivity in sulfur and selenium hydrides at high pressure

Due to its low atomic mass, hydrogen is the most promising element to search forhigh-temperature phononic superconductors. However, metallic phases of hydrogen are onlyexpected at extreme pressures (400 GPa or higher). The measurement of the recordsuperconducting critical temperature of 203 K in a hydrogen-sulfur compound at 160 GPa ofpressure [A.P. Drozdov, M.I. Eremets, I.A. Troyan, arXiv:1412.0460[cond-mat.supr-con] (2014); A.P. Drozdov, M.I. Eremets, I.A. Troyan, V.Ksenofontov, S.I. Shylin, Nature 525, 73 (2015)], shows that metallization ofhydrogen can be reached at significantly lower pressure by inserting it in the matrix ofother elements. In this work we investigate the phase diagram and the superconductingproperties of the H-S systems by means of minima hopping method for structure predictionand density functional theory for superconductors. We also show that Se-H has a similarphase diagram as its sulfur counterpart as well as high superconducting criticaltemperature. We predict H₃Se to exceed 120 K superconductivity at 100 GPa. We showthat both H₃Se andH₃S, due to thecritical temperature and peculiar electronic structure, present rather unusualsuperconducting properties.