Anomalous high-temperature superconductivity in YH6

Advanced Materials. 2021. Vol. 33. No. 15. Article 2006832.

Troyan I. A., Semenok D. V., Kvashnin А. G., Sadakov A. V., Sobolevskiy O. A., Pudalov V., Ivanova A. G., Prakapenka V. B., Greenberg E., Gavriliuk A. G., Struzhkin V. V., Bergara A., Monacelli L., Akashi R., Oganov A. R.

Pressure-stabilized hydrides are a new rapidly growing class of high-temperature superconductors which is believed to be described in terms of the Bardeen–Cooper–Schrieffer theory of conventional superconductivity. Here we report synthesis of yttrium hexahydride Im3m -YH6 that was prepared in a mixture with I4/mmm-YH4 and YH7 at pressures of 165-172 GPa via laser heating above 2400 K of metallic yttrium with ammonia borane. Compressed Im3m -YH6 demonstrates superconducting transition with TC ~ 224 K at 166 GPa, much lower than theoretical predictions (> 273 K). Upper critical magnetic field Bc2(0) of this compound was found to be 116-158 T, which is 2-2.5 times greater than the calculated one. Additional current-voltage measurements show that critical current density JC may exceed 2000 A/mm2 at 0 K, which is comparable with the parameters of commercially used superconductors such as NbTi and YBCO. Superconducting density functional theory (SCDFT) and anharmonic calculations (SSCHA) point to unusually high Coulomb repulsion (µ* = 0.19-0.21) in this compound. Discovered YH6 is the first superhydride with notable signs of a deviation of superconductivity from the Bardin-Cooper-Schrieffer theory

Keywords: high temperature superconductivity, высокотемпературная сверхпроводимость, hydrides, сверхвысокие давления, гидриды