Unveiling a novel metal-to-metal transition in LuH2: Critically challenging superconductivity claims in lutetium hydrides

Following the recent report by Dasenbrock-Gammon et al. [Nature 615, 244-250 (2023)] of near-ambient superconductivity in nitrogen-doped lutetium trihydride (LuH3−δNϵ), significant debate has emerged surrounding the composition and interpretation of the observed sharp resistance drop. Here, we meticulously revisit these claims through comprehensive characterization and investigations. We definitively identify the reported material as lutetium dihydride (LuH2), resolving the ambiguity surrounding its composition. Under similar conditions (270-295 K and 1-2 GPa), we replicate the reported sharp decrease in electrical resistance with a 30% success rate, aligning with the observations by Dasenbrock-Gammon et al. However, our extensive investigations reveal this phenomenon to be a novel pressure-induced metal-to-metal transition intrinsic to LuH2, distinct from superconductivity. Intriguingly, nitrogen doping exerts minimal impact on this transition. Our work not only elucidates the fundamental properties of LuH2 and LuH3, but also critically challenges the notion of superconductivity in these lutetium hydride systems. These findings pave the way for future research on lutetium hydride systems, while emphasizing the crucial importance of rigorous verification in claims of ambient-temperature superconductivity.