On 2023-07-30, Alex Volkov, Andrew McCalip, and Ate-a-Pi, who have been prominent in the discussion of LK-99 on Twitter, hosted a Twitter Spaces conversation of more than two hours about the status of the claims, efforts to replicate the experiments, and sources of equipment and material. The conversation actually starts at the 2:40 mark after the elevator music.
Because X/Twitter operates as a data silo, it is not possible to embed the audio recording here. What you have to do to listen is to click on the screen shot below in a browser from which you are logged into X/Twitter, then click the Play button in the purple box, then wait until the player box appears at the right, which contains controls for the player. If you do not have an X/Twitter account, you cannot play the recording.
I have only listened to brief snippets of this recording so far and cannot speak for the quality of the information therein.
On 2023-07-29, we have a theoretical paper published on arXiv, “First-principles study on the electronic structure of {\rm Pb}_{10−x}{\rm Cu}_x({\rm PO}_4)_6{\rm O}(x=0, 1)” (full text at llink), by five authors from the Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, China, exploring the electronic structure of the reported LK-99 superconductor from first-principles calculations. Here is the abstract:
Recently, Lee et al. reported the experimental discovery of room-temperature ambient-pressure superconductivity in a Cu-doped lead-apatite (LK-99) (arXiv:2307.12008, arXiv:2307.12037). Remarkably, the superconductivity persists up to 400 K at ambient pressure. Despite strong experimental evidence, the electronic structure of LK-99 has not yet been studied. Here, we investigate the electronic structures of LK-99 and its parent compound using first-principles calculations, aiming to elucidate the doping effects of Cu. Our results reveal that the parent compound {\rm Pb}_{10}({\rm PO}_4)_6{\rm O} is an insulator, while Cu doping induces an insulator-metal transition and thus volume contraction. The band structures of LK-99 around the Fermi level are featured by a half-filled flat band and a fully-occupied flat band. These two flat bands arise from both the 2p orbitals of 1/4-occupied O atoms and the hybridization of the 3d orbitals of Cu with the 2p orbitals of its nearest-neighboring O atoms. Interestingly, we observe four van Hove singularities on these two flat bands, indicating electronic instability towards structural distortions at low temperatures. Furthermore, we show that the band energies of the van Hove singularities can be tuned by including electronic correlation effects or doping with different elements. We find that among the considered doping elements (Ni, Cu, Zn, Ag, and Au), both Ni and Zn doping result in the gap opening, whereas Au exhibits doping effects more similar to Cu than Ag. Our work provides a foundation for future studies on the role of unique electronic structures of LK-99 in superconductivity.
Next, on 2023-08-01, we have a second theoretical paper up on arXiv, “Origin of correlated isolated flat bands in copper-substituted lead phosphate apatite” (full text at the link), by Sinéad M. Griffin of the Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, reporting density functional theory calculations of the LK-99 material reported to exhibit high-temperature superconductivity. Here is the abstract.
A recent report of room temperature superconductivity at ambient pressure in Cu-substituted apatite (`LK99’) has invigorated interest in the understanding of what materials and mechanisms can allow for high-temperature superconductivity. Here I perform density functional theory calculations on Cu-substituted lead phosphate apatite, identifying correlated isolated flat bands at the Fermi level, a common signature of high transition temperatures in already established families of superconductors. I elucidate the origins of these isolated bands as arising from a structural distortion induced by the Cu ions and a chiral charge density wave from the Pb lone pairs. These results suggest that a minimal two-band model can encompass much of the low-energy physics in this system. Finally, I discuss the implications of my results on possible superconductivity in Cu-doped apatite.
Here is Andrew Cote’s take on the paper, posted on Twitter within an hour of its publication.
This is the final paragraph of the “Discussion” section at the end of the original paper.
Finally, the calculations presented here suggest that Cu substitution on the appropriate (Pb(1)) site displays many key characteristics for high-{\rm T}_C superconductivity, namely a particularly flat isolated d-manifold, and the potential presence of fluctuating magnetism, charge and phonons. However, substitution on the other Pb(2) does not appear to have such sought-after properties, despite being the lower-energy substitution site. This result hints to the synthesis challenge in obtaining Cu substituted on the appropriate site for obtaining a bulk superconducting sample. Nevertheless, I expect the identification of this new material class to spur on further investigations of doped apatite minerals given these tantalizing theoretical signatures and experimental reports of possible high-{\rm T}_C superconductivity.
On 2023-08-01, we have what appears to be the first report of an apparent replication of the LK-99 room temperature superconductivity results. This was posted on bilibili.com by two researchers at the School of Materials Science and Technology of Huazhong University of Science and Technology in China, which shows partial levitation of a flake of LK-99 they report having made. The video cannot be embedded here but may be viewed at the following links:
The description of the video, translated to English by Google Translate, is:
Under the guidance of Professor Chang Haixin, postdoctoral Wu Hao and doctoral student Yang Li of the School of Materials Science and Technology of Huazhong University of Science and Technology successfully verified and synthesized the LK-99 crystal that can be magnetically levitated for the first time. Larger, it is expected to realize the real non-contact superconducting magnetic levitation.
A follow-up video, also translated by Targum.video, “Testing the sample with a magnet” purports to show testing the sample with a magnet to demonstrate it’s not ferromagnetic. I cannot see the sample in the portrait mode blur-o-vision video posted.
Here is Andrew Cote’s analysis of the first video. The original tweet included an embed of the video above which I have elided because Twitter videos cannot be embedded here.
Events of the last few days (see the three previous comments) appear to have changed the minds of punters in the prediction markets Manifold and Polymarket. (See discussion of these prediction markets in comments above: #7 [Manifold], #9 [Polymarket]).
So the materials parameter space has a theoretically identified gradient toward room temperature superconductivity which is compute-tractable, as just demonstrated by LBNL, and there hasn’t been an all-out effort to throw massive gradient descent (such as Adaptive Simulated Annealing to avoid local minima traps) ML at the problem?
And now, along comes another room-temperature superconductor patent, U.S. Patent 11,710,584 [PDF]. This appears to have nothing to do with the composition and structure of the Korean LK-99 material discussed so far. Here is the abstract of the patent.
A Type II superconductor includes a perforated carbonaceous material with an activating material on at least one surface. The activating material a non-polar liquid that does not incorporate Pi-bonding in its structure. The superconductor is manufactured by perforating a carbonaceous material to produce voids and coating at least one surface of the carbonaceous material with the activating material. A superconductive cable includes wires with a perforated carbonaceous material wetted with the activating material on a non-conductive substrate interspersed with non-conducting spacers and surrounded by an insulation layer. The superconductor conducts current at room temperature and above.
The patent application was filed on 2021-02-19 and granted on 2023-08-25. The company to which the patent is assigned, Taj Quantum, headquartered in Howey in the Hills, Florida, in the U.S. issued a press release on 2023-07-31:
Taj Quantum, a pioneer in quantum technology and blockchain-based authentication systems, is pleased to announce the awarding of a patent by the United States Patent and Trademark Office (USPTO) for its Above Room Temperature Type II Superconductor. This unique type II superconductor, patent #17249094, operates at a wide range of temperatures – including those well above room temperature, from about -100° F (-73° C) to about 302° F (150° C) – a characteristic uncommon in the world of superconductors
Inventors John Wood and Paul Lilly, renowned for their extensive work with graphene and related materials, celebrated the announcement. “We are living in thrilling times where new discoveries are being made across a variety of fields,” said John Wood. Paul Lilly added, “Our main objective is to pinpoint applications that can rapidly benefit everyone by providing the quickest-to-market capability.”
Founded originally as LGC in 2018 by Paul Lilly, Taj Quantum has grown exponentially over the past year, securing numerous contracts supporting the U.S. Military and large businesses. This superconductor patent marks a significant milestone in the company’s mission to drive scientific advancements.
“We are in an odd position holding a patent to a technology that could prove revolutionary in many fields. The last thing we want to do is gatekeep access to further scientific developments. We are working with our attorneys to develop a means to open-source our technology for Universities and non-profit groups while retaining rights associated with monetizing derivative technologies without burdening those technologies. It’s a fine line that we need to walk,” said TQ CEO Paul Lilly.
As the company continues to grow and innovate, Taj Quantum is committed to hiring a new scientific team and building associated laboratory and production facilities. They aim to bring this superconductor technology into everyday electronics over the next decade.
Note that the press release incorrectly states the patent number as “#17249094”, which is actually a garbled transcription of the patent application number, assigned at the filing on 2021-02-19, and properly stated as 17/249,094. This error has been faithfully propagated by the “journalist”-stenographers who massaged the press release into breathy media accounts.
The press release shows this picture, captioned “Taj Quantum Type II Superconductor (Graphene foam-based)”.
The picture appears to show what purports to be a superconductor partially levitating (I think it’s touching at the left) above what one supposes to be a magnet. The picture looks to have been taken on a granite countertop identical to the one in the Fourmilab kitchen.
The patent shows this drawing of a notional superconducting cable, with parts identified as…
… a superconducting unit or wire 20 with a non-conductive core or support 22, coated with a layer of activating material 24, a layer of perforated graphene 26 (e.g., wrapped therearound), and an exterior coat of activating materials 28.
Notably absent from the press release, patent, or the company Web site is any mention of experimental results confirming that this “invention” is actually a superconductor. In fact, as discovered by @CTLaw, the patent states under “Detailed Description”:
The present invention provides a type II superconductor that is operative to conduct current at a wide range of temperatures from about −100° F. (about −73° C.) to about 302° F. (about 150° C.), such as about −80° F. (about −62° C.) to about 120° F. (about 49° C.) or about −10° F. (−23° C.) to about 180° F. (about 82° C.).
which, if you read it with the right kind of eyes, doesn’t actually say it is superconductive at the stated temperatures. This would also be true of a cuprate superconductor that is superconductive at liquid nitrogen temperatures but conducts weakly and resistively within the given high temperature range.
OK, Florida Man has checked in with a room temperature superconductor. Who’s next?
Andrew McCalip, who has been working to replicate the LK-99 production process as described in comment #3, now has the results from the first attempt in hand.
Now he’s seeing partial levitation of a flake of material from the first replication sample. (Twitter videos cannot be embedded here—click the screen shot to display in 𝕏/Twitter and play: requires log-in.)
Once again, this is a “partial levitation”: one end of the flake is sitting on the bottom of the beaker. This brings to mind the remark in the theory/simulation paper discussed in comment #18 that the proposed mechanism for superconductivity only works then the copper atom binds to one of two sites in the apatite material, with the other ineffective. I wonder if the reason nobody has achieved full levitation might be that only a portion of the prepared material has the copper bound to the active location, with the rest not superconducting. The active portion drags up that part of the sample with the rest remaining on the surface.
He notes that his results are very similar to those reported by the Huazong group in China, which I discussed in comment #19, and in the following comment here.
The group at Huazhong University of Science and Technology in China who reported replication of LK-99 synthesis and observed partial levitation in a video noted here in comment #19 have now posted a report of their work on arXiv (full text at link):
Here is the abstract:
Recently, Sukbae Lee et al. reported inspiring experimental findings on the atmospheric superconductivity of a modified lead apatite crystal (LK-99) at room temperature (Consideration for the development of room-temperature ambient-pressure superconductor (LK-99) -Journal of the Korean Crystal Growth and Crystal Technology | Korea Science, arXiv: 2307.12008, arXiv: 2307.12037). They claimed that the synthesized LK-99 materials exhibit the Meissner levitation phenomenon of superconductors and have a superconducting transition temperature (Tc) higher than 400 K. Here, for the first time, we successfully verify and synthesize the LK-99 crystals which can be magnetically levitated with larger levitated angle than Sukbae Lee’s sample at room temperature. It is expected to realize the true potential of room temperature, non-contact superconducting magnetic levitation in near future.
Here is a paper from three authors at the Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Science who prepared a sample of LK-99 according to the instructions in the original papers and tested it.
Here is the abstract:
Lee et al. reported that the compound LK99, with a chemical formula of {\rm Pb}_{10}−_x{\rm Cu}_x({\rm PO}_4)_6{\rm O}(0.9<x<1.1), exhibits room-temperature superconductivity under ambient pressure. In this study, we investigated the transport and magnetic properties of pure {\rm Cu}_2{\rm S} and LK-99 containing {\rm Cu}_2{\rm S}. We observed a sharp superconducting-like transition and a thermal hysteresis behavior in the resistivity and magnetic susceptibility. However, we did not observe zero-resistivity below the transition temperature. We argue that the so-called superconducting behavior in LK-99 is most likely due to a reduction in resistivity caused by the first order structural phase transition of {\rm Cu}_2{\rm S} at around 385 K, from the β phase at high temperature to the γ phase at low temperature.
They conclude:
In conclusion, we measured transport and magnetic properties of pure {\rm Cu}_2{\rm S} as well as the mixture LK-99/{\rm Cu}_2{\rm S}, and reproduce the experimental results of resistivity. We found a sharp drop in resistivity, however, none of them show zero-resistivity. The superconducting-like behavior in LK-99 most likely originates from a magnitude reduction in resistivity caused by the first-order structural phase transition of {\rm Cu}_2{\rm S}.
Would it be fair to assume that the net benefit is drawing attention to the possibility of creating low resistance materials relying on the peculiar configuration identified with LK99?
A whole industry dedicated to selectively doping semiconductor substrates emerged in the 1960s and became the underlying support for the massive industrial and technological advances made possible by microprocessors.
I imagine LK99 type materials hold a lot of potential even if it turned out it’s not a bona fide superconducting material.
