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The myth of room temperature superconductivity in LK-99 is busted

Date:27-11-2023 Print

Sukbae Lee et al from South Korea claimed that the Pb10-xCux(PO4)6O (0.9<x<1.1), dubbed LK-99, is a superconductor at ambient pressure with Tc up to 127°C (400 K). The shocking news stimulates scientists and people on social media due to its potential impact on technology. As Nature News reported, it has become a viral sensation and prompted a slew of replication efforts by scientists and amateurs alike. Several groups attempted to replicate the results, but none provided direct evidence for superconductivity. The most mysterious is what the sharp decrease in resistivity comes from and why it only appears in a few samples.

A team from the IOP of CAS led by Prof. LUO Jianlin noted that the LK-99 made by Lee et al contained a certain amount of Cu2S impurity, which undergoes a structural phase transition from the hexagonal structure at high temperature to the monoclinic structure at low temperature near 400 K. They found that the resistivity of Cu2S decreased by 3 - 4 orders of magnitude around 385 K, close to the reported transition temperature in references. Additionally, they measured the resistivity of the mixture of LK-99 and Cu2S, which showed a sharp resistivity transition at the temperature consistent with the reported findings, but without zero resistance.

It is important to note that this first-order structural transition differs significantly from the second-order superconducting transition. They observed a thermal hysteresis behavior in the resistivity and magnetic susceptibility measurements, which proves it is a first-order transition and cannot be a second-order superconducting transition. The findings strongly suggest the superconducting-like transition in LK-99 as reported by Lee et al. originates from the first-order structural transition of the impurity phase of Cu2S.

Their results provide solid evidence that LK99 is non-superconducting and put an end to the rumors.

This study entitled "First order transition in LK-99 containing Cu2S" was published on Matter.

The study was supported by the National Natural Science Foundation, the Ministry of Science and Technology of China, and the Chinese Academy of Sciences.

Fig.1 Temperature dependence of resistivity of Cu2S, LK-99 including Cu2S (Image by Institute of Physics) 

Institute of Physics
LUO Jianlin

Key words:
LK-99, Cu2S, room temperature superconductivity

Lee et al. reported that the compound LK-99, with a chemical formula of Pb10-xCux(PO4)6O (0.9<x<1.1), exhibits room-temperature superconductivity under ambient pressure. In this study, we investigated the transport and magnetic properties of pure Cu2S and LK-99 containing Cu2S. We observed a sharp superconducting-like transition and a thermal hysteresis behavior in the resistivity and magnetic susceptibility. However, we did not observe zero resistivity below the transition temperature. We argue that the so-called superconducting behavior in LK-99 is most likely due to a reduction in resistivity caused by the first-order structural phase transition of Cu2S at around 385 K, from the hexagonal structure phase at high temperature to the monoclinic structure phase at low temperature.