Enhancement of superconducting properties in the La–Ce–H system at moderate pressures

Abstract

Compressed polyhydrides have been regarded as an important platform for exploring high-temperature superconductors. The disordered states with high entropy could possess better superconducting properties than conventional periodic structures. Here, we have discovered a new high entropy superconducting La–Ce polyhydride (initial ratio La: Ce = 2.5–3.5:1), which is stable under low pressures with the giant enhancement of superconducting properties compared with the binary La-H and Ce-H system. Its superconductivity at 176 K was strikingly preserved to about 100 GPa, and the extrapolated upper critical field Hc2(0) reached 235 T, both of which are the record values among the synthesized polyhydrides at 100 GPa. We also performed the contrast experiments on binary lanthanum hydride that show a much lower Tc (up to 100 K) at the same pressure range. The experimental results and theoretical calculation indicate the disordering state of the La-Ce-H system with high configurational entropy. The aroused configurational entropy shifts the La-Ce-H system towards a dirty limit that not only enhanced the stability but also improved the superconducting properties by softening the phonon frequency (ω), shorting the electron mean free path (ℓ), and increasing the electron-phonon coupling parameter (λe−p). These results show how better superconductors can be engineered in this new class of hydrides.

Magnetic flux trapping in hydrogen-rich high-temperature superconductors

“…22), La-Nd (ref. 23) and 24) binary alloys was studied, but without a noticeable enhancement in T c and pressure range of stability of presumably ternary final superhydrides compared with the parent binary Fm-3m-LaH 10 and P6 3 /mmc-LaH ~9-10 phases 8 .…”

High-temperature superconductivity up to 223 K in the Al stabilized metastable hexagonal lanthanum superhydride

“…Comparing these experimentally obtained cell volumes with previous experimental and theoretical results, we tentatively propose that the ratio of metal to hydrogen in the obtained compound is 1:10. Recently, our group also observed a hexagonal phase for the binary La–H system at 130 GPa, but the exact ratio is unknown [ 42 ]. According to the theoretical calculations for the binary La–H system, the P 6 3 /mmc -LaH 10 structure becomes thermodynamically favorable at pressures above ∼420 GPa; more importantly, this P 6 3 /mmc phase is also considered possibly metastable at low pressures and previous theoretical work has indicated that this phase was lying within the 20-meV/atom of the Fm \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} $\bar{3}$\end{document} m phase down to 150 GPa [ 17 ].…”

Superconducting Be2SH3 with kagome hydrogen at high pressure

“…29 Yet, thus far, only a few ternary hydrides have been experimentally synthesized, including the low- T c of BeReH 9 (7 K at 100 GPa) 30 and Li 5 MoH 11 (6.5 K at 160 GPa). 31 Recently, experimentalists have successfully synthesized several high- T c ternary hydrides (La,Y)H 10 (253 K at 183 GPa), 32 (La,Ce)H 9 (178 K at 110 GPa or 176 K at 100 GPa) 33,34 and (La,Nd)H 10 (148 K at 170 GPa), 35 which further demonstrates the superconductive potential of ternary hydrides. Of these, superconductors based on sulfur hydride have been abundantly reported, such as C–S–H, 36–39 Y–S–H, 40,41 Se–S–H, 42 B–S–H, 43 Fe–S–H, 44 Ca–S–H, 45 even including noble gases like Xe–S–H.…”