Why did the 2023 LK-99 room-temperature superconductor claim collapse within weeks?

The claim collapsed because it never showed the signatures that define a superconductor, and because other scientists found ordinary explanations for what it did show. In July 2023 a Korean team published preprints claiming that LK-99 was a room-temperature superconductor at up to 400 K at ambient pressure. Researchers reached initial results within weeks, and by mid-August 2023 the consensus was that LK-99 is not a room-temperature superconductor and is an insulator in pure form.

The claim was extraordinary. At the time, the best known superconductors reached 250 K only at enormous pressure, and at atmospheric pressure at most 150 K. And the preprints did not report any definitive property of superconductivity, such as zero resistance, the Meissner effect or a jump in specific heat. What they offered instead was a tiny sample that seemed to float partly over a magnet.

That partial levitation is a sign of ordinary diamagnetism or ferromagnetism, but a video of it went viral, with memes about floating rocks and a brief surge in Korean and Chinese technology stocks. A prediction market briefly put the chance of successful replication at 60%.

Then the replications came in. A prominent cause of the signs was a copper sulfide impurity from the recipe, which can produce resistance drops, a heat-capacity transition and magnetic response in small samples. On 16 August 2023, Nature published an article declaring that LK-99 had been shown to be an insulator, not a superconductor. It is a case of science working fast: a bold claim, quickly tested, and quickly corrected.