An Exciting Week in Material Science
By Shawn Lee.
Some intriguing claims by Korean superconductor researchers hold lessons ion the importance of verification in academia and in industry.
Alleged partial levitation of an LK-99 sample [1]
On Friday afternoon, three Korean researchers released two pre-prints (draft papers not yet reviewed by third party peers or editors) claiming to have made a superconductor that works at room temperature and pressure [2]. This is an exciting claim; superconductors can conduct electricity without any resistance or loss. In theory, these materials could dramatically increase the efficiency of electricity transmission and electronics, low-friction transport, nuclear fusion, and quantum computing. In practice, all currently published superconducting materials only show their special properties at very low temperatures. In 2021, the highest temperature superconductor was a fragile cuprate of mercury, barium, and calcium at -140C.
Assessing claims of high temperature superconductivity in public is similar to how we assess claims of technical performance at New Energy Risk. Like many exciting developments, the record around this possible discovery is still emerging. The original papers were the product of a collaboration between a university professor and industrial R&D postdocs. One of the original two papers drafts was recalled, and the author who originally brought it to the public turns out had been fired a while ago. The industrial partners may have held back key parts of the manufacturing recipe, or at the very least released a substantially non optimal study [3].
There are two aspects of a technical claim that need to be validated. The first is theoretical: is the claim possible under the laws of physics, and under what conditions? The second part is empirical: can we show with data that this really happened? On the theoretical side, the original paper speculated, without quantum-mechanical simulations, that adding trace amounts of copper caused the material structure to deform enough to create superconducting states. On Monday, teams from Argonne National Lab and Northwest University in Xi’an both ran density functional theory quantum simulations that showed two possible reasons why room temperature superconductivity could be possible with materials in the original paper [4]. This is interesting because prior to this, superconductors generally came from altered conductors, whereas the base material before copper addition here, apatite, is an insulator, and both papers showed that while the superconducting state is possible, it competes with non-superconducting states and is not preferred.
Simulated distortions by substituting Copper centers [5]
On the experimental side, the original papers did not actually measure zero electrical resistance or the full expulsion of the magnetic field from the material that would be key signs of superconductivity, but did include partial levitation on top of a magnet, which could indicate regions of superconductivity at room temperature. Unlike most other superconducting candidates, these materials can be produced over the course of days. The fanciest piece of equipment necessary is a chemical vapor deposition chamber, which is common in most semiconductor labs and means that we should have results from third parties within a week.
The first experimental results from third parties are a mixed bag. The first one in pre-print, from Beihang University, showed no sign of superconductivity at room temperature as claimed, while claiming a purer version of the material than the original Korean papers [6]. Other results announced, but not written up, show mixed results ranging from optimistic to no noticeable effects at all, with the most optimistic case showing as zero resistance at 110K (well below the originally advertised transition temperature) [7]. Nothing, including the original papers, has been peer reviewed, but even that’s not a guarantee. In 2022, another team’s high temperature superconducting paper had to be retracted from Nature after publication because of falsified data.
Between the theory and the mixed bag of early experimental results, it’s certainly interesting enough to continue investigating. My guess right now is there may be some local states which may display some superconducting characteristics, but the difficulty in isolating those regions may make replication harder than in other materials. As the picture of what’s actually happening in these materials emerges, we see similar themes to how NER underwrites any new technology: we make sure it’s physically possible at least in theory – even if the precise causal mechanism is unknown – and then we make sure that key claims have been validated experimentally by third parties, and that the method reporting is sound and consistent with best standards.
That’s clearly not yet the case here. There are probably years of process engineering improvements and characterizations before a verified discovery becomes an insurable commercial technology, but this is a reminder of the importance of verification procedures, both in academia and in industry.
Cited Works
[1] https://arxiv.org/ftp/arxiv/papers/2307/2307.12037.pdf
[2] https://arxiv.org/ftp/arxiv/papers/2307/2307.12008.pdf
[3] https://www.tomshardware.com/news/superconductor-breakthrough-replicated-twice
[4] https://arxiv.org/abs/2307.16892 and https://arxiv.org/abs/2307.16040
[5] https://arxiv.org/pdf/2307.16892