  Following the recent report by Dasenbrock-Gammon et al. (2023) of
near-ambient superconductivity in nitrogen-doped lutetium trihydride
(LuH3-{\delta}N{\epsilon}), 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
Dasenbrock-Gammon et al.'s observations. 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.
