Superconductivity is a condition of matter where resistance to electrical current disappears.
The first superconductors needed cooling to near the absolute zero. The next generation worked at temperatures of liquid nitrogen. A room-temperature atmospheric-pressure superconductor is a highly sought after material (e.g. it would expand possibilities to hande plasma for fusion research and make MRI machines easier to build).
A substance named LK-99 has recently caused interest in the research community. Its a copper-enriched lead apatite, typically made by reacting lead sulphate with copper phosphide. It is speculated to be superconductive at room temperature.
It is also thought that interesting properties are not inherent to the substance, but a particular kind of crystal lattice which this subtance obtains - if produced in certain ways.
The name LK-99 refers to Sukbae Lee and Ji-Hoon Kim, and the number refers to 1999, when these Korean researchers first stumbled upon it.
Studies back then were interrupted. They weren't certain of its properties and it was hard to make repeatably. When a researcher named Tong-Shik Choi died in 2017, he requested in his will that research into LK-99 be continued. The resources were found and his request was granted.
Then, other factors intervened, among them COVID. The first article was rejected by Nature because an extraordinary claim requires extraordinary proof. An article in Arxiv (not peer reviewed) at the end of July 2023 drew international attention, however.
Many persons and teams started attempting to replicate the experimental results. The process is still half way through, but considerable progress has been made.
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Beijing University, school of material science + Beihang university: the experiment was made, but the effect could not be reproduced (they obtained a paramagnetic semiconductor of little interest)
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Huazhong University, center for crystalline materials and micro/nanodevices: they obtained a diamagnetic crystal with interesting properties (repelled by a ferromagnet regardless of orientation, a property which a superconductor must have, but which is also shared by non-superconductive diamagnets)
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National Physics Laboratory of India: failed to replicate the effect
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Professor Sun Yue, South-Eastern University of China: got a weak diamagnetic crystal
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Iris Alexandra (from Russia, plant physiologist): with an alternative production method, obtained a tiny but strongly diamagnetic crystal
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Sinéad Griffin (Lawrence Berkley National Laboratory, from the US): published an article, attempting to theoretically explain how superconductivity might arise in the substance, explanatory tweet here
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Junwen Lai (Shenyang National Material Science Laboratory, China): published an article about the electron structure of the substance, without opinion regarding superconductivity, with the opinion that gold doping would be better than copper doping
So, strong evidence is absent until now - we may have much merriness about nothing. There is a bunch of hypothesis and enough material to fit on a fingertip. :)
Background: