Superconducting H(5)S(2) phase in sulfur-hydrogen system under high-pressure

Recently, hydrogen sulfide was experimentally found to show the high superconducting critical temperature (T(c)) under high-pressure. The superconducting T(c) shows 30–70 K in pressure range of 100–170 GPa (low-T(c) phase) and increases to 203 K, which sets a record for the highest T(c) in all materials, for the samples annealed by heating it to room temperature at pressures above 150 GPa (high-T(c) phase). Here we present a solid H(5)S(2) phase predicted as the low-T(c) 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 H(5)S(2) phase is thermodynamically stabilized at 110 GPa, in which asymmetric hydrogen bonds are formed between H(2)S and H(3)S molecules. Calculated T(c) values show 50–70 K in pressure range of 100–150 GPa within the harmonic approximation, which can reproduce the experimentally observed low-T(c) phase. These findings give a new aspect of the excellent superconductivity in compressed sulfur-hydrogen system.