Pressure‐stabilized hydrides are a new rapidly growing class of high‐temperature superconductors, which is believed to be described within the conventional phonon‐mediated mechanism of coupling. Here, the synthesis of one of the best‐known high‐TC superconductors—yttrium hexahydride ‐YH6 is reported, which displays a superconducting transition at ≈224 K at 166 GPa. The extrapolated upper critical magnetic field Bc2(0) of YH6 is surprisingly high: 116–158 T, which is 2–2.5 times larger than the calculated value. A pronounced shift of TC in yttrium deuteride YD6 with the isotope coefficient 0.4 supports the phonon‐assisted superconductivity. Current–voltage measurements show that the critical current IC and its density JC may exceed 1.75 A and 3500 A mm−2 at 4 K, respectively, which is higher than that of the commercial superconductors, such as NbTi and YBCO. The results of superconducting density functional theory (SCDFT) and anharmonic calculations, together with anomalously high critical magnetic field, suggest notable departures of the superconducting properties from the conventional Migdal–Eliashberg and Bardeen–Cooper–Schrieffer theories, and presence of an additional mechanism of superconductivity.
Troyan, I. A., Semenok, D. V., Kvashnin, A. G., Sadakov, A. V., Sobolevskiy, O. A., Pudalov, V. M., Ivanova, A. G., Prakapenka, V. B., Greenberg, E., Gavriliuk, A. G., Lyubutin, I. S., Struzhkin, V. V., Bergara, A., Errea, I., Bianco, R., Calandra, M., Mauri, F., Monacelli, L., Akashi, R., Oganov, A. R., Anomalous High‐Temperature Superconductivity in YH6. Adv. Mater. 2021, 33, 2006832. abstract
a) XRD pattern of the sample in DAC K1 at 166 GPa collected at a wavelength λ = 0.334 Å. b) Le Bail refinements of ‐YH6, Imm2‐YH7, and P1‐YH7+z (z = ±0.5) at 166 GPa. Unidentified reflections are marked by asterisks. c) XRD pattern of the M3 sample at 172 GPa collected with λ = 0.295 Å. d) Le Bail refinements of ‐YH6 and I4/mmm‐YH4. The experimental data, fitted line, and residues are shown in red, black, and green, respectively. e,f) Crystal structures of YH4 and YH6.