Inspenet, December 27, 2023.
In a study published last month in Matter, a team of researchers led by Prof. Luo Jianlin of the Institute of Physics of the Chinese Academy of Sciences (CAS) presented strong evidence indicating that LK99 does not exhibit superconducting properties, thus contradicting claims previous reports on its superconductivity.
Previously, Sukbae Lee and his South Korean colleagues had claimed that LK99 acted as a superconductor at room pressure , with a critical temperature (Tc) reaching up to 127°C (400 K). This groundbreaking news generated great excitement among both scientists and social media due to its potential impact on technology.
As reported by Nature News, claims about the compound’s supposed superconductivity went viral, generating numerous replication attempts by scientists and hobbyists alike. Despite efforts by several groups to reproduce the results, none have so far presented direct evidence of superconductivity. The most puzzling question is what causes the marked decrease in resistivity and why it occurs only in some samples.
LK99’s “superconductivity” came to an end
In this study, the researchers observed that the LK99 generated by Lee and colleagues contained a significant amount of Cu2S impurity, which undergoes a structural phase transition from a hexagonal structure at high temperature to a monoclinic structure at low temperature around 400 K. They discovered that The resistivity of Cu2S decreased between three and four orders of magnitude around 385 K , close to the transition temperature reported in the references.
Additionally, they carried out resistivity measurements of the combination of LK99 and Cu2S, identifying an abrupt transition in resistivity at a temperature consistent with previously reported discoveries, but without reaching zero resistance.
It is essential to highlight that this first-order structural transition differs markedly from the second-order superconducting transition. The researchers observed thermal hysteresis behavior in resistivity and magnetic susceptibility measurements, confirming that it is a first-order transition and cannot be considered a second-order superconducting transition.
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