  Since the discovery of superconductivity in mercury at 4 K in 1911, searching
for materials with superconductivity at higher temperatures towards practical
conditions has been a primary enduring goal. The recent report of
room-temperature superconductivity at near-ambient pressure in nitrogen-doped
lutetium hydride (Lu-H-N) by Dasenbrock-Gammon et al. (Hereafter referred as
D-G) seems a great step approaching the ultimate goal. Specifically, they
claimed evidence of superconductivity on Lu-H-N with a maximum Tc of 294 K at 1
GPa. However, the failure to observe the drastic temperature-dependent
resistance change above 200 K in high-pressure synthesized Lu-H-N compounds, a
prerequisite for superconductivity, by researchers worldwide in all independent
follow-up studies casts a heavy shadow on the authenticity of the claims. The
sober questions are: what is the sample that produces the sharp resistance jump
near room temperature? What are the reasons for the non-reproducibility of
others who follow the D-G method of synthesis and the inscrutable low success
rate (35%) in synthesizing the right sample even for the authors in Ref. 1?
What causes the observed sharp resistance jump? Here, with a well-controlled
experiment protocol, we repeatedly reproduced the near room-temperature sudden
change of electrical resistance in the Lu-H-N sample, and we could
quantitatively compare its behavior with the initial pure Lu in a normal
metallic state. These results enable us to scrutinize the origin for the
near-room temperature sharp resistance change, which is attributed to a
metal-to-poor-conductor transition rather than superconductivity.
