On 2023 July 22nd, two papers have submitted to the arXiv, which declared that they finished the world's first room temperature ambient pressure superconductor called LK-99 (https://arxiv.org/ftp/arxiv/papers/2307/2307.12008.pdf, https://arxiv.org/ftp/arxiv/papers/2307/2307.12037.pdf). Along with the paper, a video of the suspension is also attached, which attracted wide interest on the internet through We Media. On July 28th, one of the authors gave a talk at the Metalic Multilayers Conference (MML23) to introduce the work but did not show the sample. They declared that Lee and Kim discovered the materials in 1999, and Prof. Kwon from Korea University attended them in 2018. They invited Hyun-Tak Kim to attend in 2021 and published a paper in a Korean journal in April 2023. Till now, one of the arXiv papers has been withdrawn, and the author declared they plan to submit the results to APL materials via Twitter. Some information from the internet mentioned that some groups are repeating the sample, but no official information has been found till now.

This is not the first-time room temperature has been reported. The most famous one is the two papers on Nature, in which the materials are C-S-H and Lu-N-H. Both of them come from Ranga Dias. The C-S-H paper is already retracted. Prof. Haihu Wen also published a paper to show the absence of superconductivity in the Lu-N-H system in nature, but Prof. Russell J. Hemley showed the data to support Dias in arXiv (https://arxiv.org/ftp/arxiv/papers/2306/2306.06301.pdf). C-S-H and Lu-N-H only show superconductivity under pressure instead of ambient pressure, as mentioned by the Korean group. The room temperature ambient pressure superconductor is contradictory with existing superconducting theories. But even so, it is not the first time to be reported on arXiv. In 2016, one person from India published a paper on arXiv to show the room temperature ambient pressure superconductor (1603.01482.pdf (arxiv.org)).

The new superconductor reported by the Korean group is doubtful for two primary reasons

The first and most important is the suspension video. The suspension of a superconductor is due to the flux pinning. It causes when the superconductor suspends on the magnet (the magnet suspends on the superconductor in most demonstrations), it is tough to move the superconductor. After a slight touch on the superconductor, it will go back to the original position instead of any displacement. However, in the video from the Korean group, they easily moved the LK-99 bulk after suspension. Moreover, the LK-99 is not a complete suspension on the magnet but with an edge attached to the magnet. So the suspension of the LK-99 is completely different from the superconductor.

The second is data on resistivity. The zero resistance is the symbol of the superconductor. However, the paper did not give strong evidence for the zero resistance Fig. 5 in https://arxiv.org/ftp/arxiv/papers/2307/2307.12037.pdf has the scale of resistivity of 1E−2 Ω cm, which is definitely not low enough to show the zero resistance phenomenon. Fig. 6 shows an obvious non-zero voltage signal, and the minimum resistance could be around 15 mΩ at 20 °C. It is not even can be called a small resistance.

Beyond these two reasons, the theory of the room temperature ambient pressure superconductor from the Korean group is also very strange, which are “the first being the volume contraction resulting from an insulator-metal transition achieved by substituting Pb with Cu, and the second being on-site repulsive Coulomb interaction enhanced by the structural deformation in the one-dimensional (D) chain (Pb2-O1/2-Pb2 along the c-axis) structure owing to superconducting condensation at Tc. The mechanism of the room-temperature Tc is discussed by 1-D BR-BCS theory.” According to my acknowledgment, the “1D superconducting chain” has never been found in previous research papers. The theoretical derivation given by the author on this 1D chain is not convincing. The volume restriction is also not fully proven because the XRD result is low quality. The crystal volume from such an XRD result cannot be fully trustable. Furthermore, how to form volume restrictions in long-range ordering is also doubtful.

Why does such an arXiv paper attract much attention from common people? Maybe it is because most people believe the room temperature can change the world and their life. Unfortunately, the answer is that even if we have the real room temperature ambient pressure superconductor, it probably will not change our life. The critical transition temperature is neither the only critical parameter nor the most important parameter for the superconductor. Many state-of-the-art technologies, such as high-field MRI, fusion Tokamak, and quantum computers, use the superconductor as the primary component. However, they all work at a much lower temperature than the critical transition temperature of the superconductor they used.

For large-scale application scenarios, such as MRI, NMR, power transmission, Maglev, wind generator, fusion Tokamak, etc., all of them primarily require the superconductor to carry large current, which means high critical current density, especially under applied field. Beyond the current capability, the superconductor should easily form wires or tapes in long lengths. So in the real application, much less attention was given to the temperature. That is why NbTi, whose transition temperature is less than 10 K, still occupies 95% of the market share.

For the device application, such as quantum computers, single photon detectors, SQUID, etc., the high temperature itself is harmful to the performance device. For example, quantum computers need to work at 10 mK, which is not due to the transition temperature of the superconductor but the requirement of the quantum computer itself.

So, a new superconductor with only a transition temperature above room temperature cannot change the world directly. It may help the scientists to understand the mechanism of superconducting better. The improved theory may guide the scientists to explore new superconductors that may carry large currents under room temperature.