The encyclopedia · R&D & Science · Strategic decision · 2023
LK-99: the 'world-first' superconductor that was copper sulfide and iron
Two preprints claimed the first room-temperature superconductor. Three weeks of global hype later, the miracle was copper sulfide impurities and a bit of iron.
Quantum Energy Research Centre · Korea University · 2023-07-22
What happened
On 22 July 2023 two preprints appeared on arXiv from the Quantum Energy Research Centre, a small Seoul start-up run by Lee Sukbae and Kim Ji-Hoon. Their material, LK-99 — a copper-doped lead apatite named for Lee, Kim and the year 1999, when they began studying it at Korea University — was, they said, 'for the first time in the world', a superconductor at room temperature and everyday pressure, up to 127 °C.
The claim went global within days. Prediction markets briefly gave replication a 60% chance; a Huazhong University video of a sample 'partially levitating' went viral on Chinese social media; the team sent a second video to the New York Times; Korean and Chinese 'superconductor stocks' surged so hard the Korean exchange warned against speculative bets. Scientists asked to test a sample. The team said it would share one only after its own journal review was complete — as physicist Michael Fuhrer put it, 'there are many ways to get fooled'.
Replication did not wait for permission. A dozen labs failed to reproduce the effect within three weeks; Southeast University's reported resistance drop below 110 K was rejected by experts; Peking University found no Meissner effect and no zero resistance. The Korean Society of Superconductivity set up a verification committee, and the explanation emerged by mid-August: the dramatic resistivity drop came from a copper sulfide impurity with a phase transition near 104–127 °C, and the 'levitation' from ferromagnetic iron flecks. On 16 August Nature declared LK-99 not a superconductor.
The preprints were never formally retracted. In November the Chinese Academy of Sciences published its impurity analysis in the journal Matter — 'another nail in the coffin' — concluding the superconductivity-like behaviour was caused by the structural phase transition of copper sulfide. LK-99 went from Nobel talk to cautionary tale in under a month: the price of announcing a 24-year result with no sample anyone else could hold.
Why it happened
- Announced before verified: two unreviewed preprints, a 'world first', and no sample anyone could test — the claim outran the evidence before the world could answer.
- The team was split before the world even replied: a co-author said the first paper contained 'many defects' and was uploaded without his permission.
- The show outran the science: the levitation and the resistance drop were consistent with mundane physics — a copper sulfide phase transition and iron impurities — that controls would have caught.
- Refusing to share samples let speculation fill the vacuum: prediction markets, viral videos and a stock frenzy ran for weeks while the only people who held the material guarded it.
The lesson
Extraordinary claims need a sample, not a preprint. The world held nothing, so it filled the gap with viral videos and a stock frenzy — until copper sulfide explained everything.
Aftermath
The preprints were never formally retracted and the journal submission stayed in limbo; the team blamed each other instead. In November 2023 the Chinese Academy of Sciences published its impurity analysis in Matter, concluding the superconductivity-like behaviour came from the structural phase transition of copper sulfide — 'another nail in the coffin'. The Korean verification committee's verdict was that no evidence supported the claim. LK-99 became shorthand for hype, and the material itself — a real purple lead apatite — conducts like a rock.
Sources
- Wikipedia — LK-99 (full timeline: preprints, replication attempts, Cu2S and iron explanation, stock effects, verification committee)
- The Guardian — 'There's no room-temperature superconductor yet, but the quest continues' (2 Sep 2023, retrospective with Fuhrer and Hirsch)
- ScienceAlert — 'LK-99 Is No Radical Superconductor After All, Scientists Confirm' (30 Nov 2023, CAS impurity analysis published in Matter)
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