Leading components and pressure-induced color changes in N-doped lutetium hydride

TL;DR

This study uses density functional theory to identify the main components of N-doped lutetium hydride, explains its pressure-induced color changes, and clarifies why superconductivity was not observed in follow-up experiments.

Contribution

It provides a detailed theoretical analysis of the composition, structural changes, and electronic properties of N-doped lutetium hydride, explaining the absence of superconductivity.

Findings

LuH₂ is the major component with minor LuN.

Color changes from blue to purple and red under pressure due to hydrogen vacancies.

Density of states at the Fermi level is dominated by Lu-5d orbitals, not supporting superconductivity.

Abstract

Recent experimental study by Dias {\it et al.} claims to have discovered room-temperature superconductivity in lutetium-nitrogen-hydrogen system at 1 GPa [Nature 615, 244 (2023)], which sheds light on the long-held dream of ambient superconductivity. However, all follow-up experiments found no evidence of superconductivity. The compositions and the crystal structures of the lutetium-nitrogen-hydrogen system remain unknown. By employing the density functional theory based structure prediction algorithm, we suggest that in lutetium-nitrogen-hydrogen the major component is LuH$_2$ (Fm$\bar{3}$m), together with minor LuN (Fm$\bar{3}$m). The blue LuH$_2$ at ambient pressure will turn into purple and red color at higher pressures, possibly accompanied by the formation of vacancies at hydrogen-sites. In LuH$_2$ and LuN, the density of states at the Fermi level is dominated by the Lu-5d orbitals, while those from hydrogen and nitrogen are very small, leading to the absence of superconductivity in these two compounds. Nitrogen-doping to LuH$_2$ fails to enhance the superconductivity as well. In this work, we identify the leading components in N-doped lutetium hydride, explain its intriguing color changes under pressure, and elucidate why superconductivity is absent in the follow-up experiments.