Paul van Gerven
23 August 2023

Consensus among scientists is rapidly growing that social-media hit LK-99 is, in fact, not a superconductor at room temperature and ambient pressure. An article published by Nature News sums up the failed attempts to replicate the findings and, more importantly, gives a convincing explanation for the observations made by the Korean scientists, who published their preliminary findings – along with LK-99’s recipe – on the Arxiv pre-print server in July.

The Korean team at Quantum Energy Research Center, a small company operating from a basement in Seoul, based its superconductivity claim on the observation that the electrical resistance of LK-99 dropped sharply at a certain temperature and the fact that the material (partially) levitated above a magnet. Both are hallmarks of a superconductor.

LK 99 pellet
This piece of LK-99 is (partially) being repelled by a magnet. Credit: Hyun-Tak Kim via Arxiv

By now, however, dozens of attempts to confirm LK-99’s superconductivity have failed. What’s more, the reported transition temperature of about 105 degrees Celsius rang a bell with many scientists: it’s close to the temperature at which pure copper sulfide’s resistance changes drastically (but not to zero). Synthesizing LK-99 requires copper and sulfur compounds to be mixed in such a way that the formation of copper sulfide is likely.

Only two weeks after the initial publication, a team at the Chinese Academy of Sciences already argued that the “the so-called superconducting behavior in LK-99 is most likely due to a reduction in resistivity caused by a structural phase transition of copper sulfide.” Other experts have since chimed in that the Koreans have most likely observed low (but not zero) resistance in a material that contains copper sulfide.

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The partial levitation also has a more mundane explanation: ferromagnetism can also cause this effect. A former condensed-matter researcher at Harvard University posted a video on X (formerly Twitter) in which he replicates LK-99’s ‘half-floating’ behavior using nothing but iron shavings and graphite.

“While nobody has proven that the LK-99 samples studied in the original reports don’t superconduct, the balance of evidence right now is strongly in favor of other explanations. Most scientists studying superconductivity don’t see much reason to continue looking at LK-99,” concludes Monash University physicist Michael Fuhrer on The Conversation.