Anomalous High‐Temperature Superconductivity in YH₆

Abstract

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 Im3¯m‐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.

Superconductivity up to 243 K in the yttrium-hydrogen system under high pressure

“…2a ) and the c / a ratios of bct- YH 4 and hcp -YH 9 (Fig. 2b ) agree well with the theoretical predictions 22 – 24 , 26 , 31 , 32 , which justifies the assignment of compositions for the hydrides with H/Y > 3.…”

“…Here, we also discuss the contradictions between different experimental data for the yttrium-hydrogen system. Our preliminary report 25 and the present more comprehensive data are in good agreement with the data from Troyan et al 26 but evidently contradict the claim of T c = 262 K at 182 GPa reported by Snider et al 27 .…”

“…Open black circles, stars, squares and triangles correspond to the theoretically predicted structures for YH 9 22 , YH 6 22 – 24 , 26 , YH 4 22 – 24 , 26 and YH 3 31 , 32 , respectively. Experimental data for pure Y 33 , 63 , YH 3 59 , YH 4 26 and YH 6 26 taken from the literature are depicted by the red symbols. Solid curves correspond to the Vinet 30 equation of state fitting.…”

“…Cyan, magenta and grey curves are the guides for the eye. Brown squares depict the data from Troyan et al 26 . Error bars are defined the same as in Drozdov et al 12 .…”

Topological polarization, dual invariants, and surface flat bands in crystalline insulators

“…Other current participants in the race are hydrogen-rich materials, such as H 3 S, LaH 10 , Li 2 MgH 16 , YH 6 , etc. [81][82][83][84][85]. In these systems, the large transition temperature results from the large vibrations of light hydrogens, which increase the electron-phonon coupling.…”