Korean researchers report an ambient temperature and unpressured material that possesses superconductivity (Lee, Kim, Kwon Korea University, ). Much sought after by a multitude of research groups for the past 40 years, the claim will certainly meet a lot of scrutiny. That search was kick started with the material lanthanum barium copper oxide found to exhibit superconductivity at 37 kelvin in 1987. The current record as far as ambient-pressure materials is concerned is 150 Kelvin for the compound HgBa2Ca2Cu3O established in 1993. This blog has covered various efforts, one from 2010 for an(organic superconductor) and a notorious one from 2020 with involved a carbon-sulfur material and a retraction (link).

It is not that the new material is difficult to make. Lanarkite (Pb2(SO4)O) is an unremarkeble mineral that can be found in certain Scottish hills. A synthetic variety was made by mixing lead oxide and lead sulfate in a mortar and pestle and heating at 725 degrees celsius. Copper phosphide (CuP3) is a material commonly used in certain forms of metallurgy and was custom-prepared from the corresponding elements and heating at 550 degrees and a vacuum. For the synthesis of the superconductor The lead sulfate was mixed with the copper phosphide and heated at 925 degrees at a high vacuum leaving an approximate Pb9Cu(PO4)6O material.

And superconducting? As main exhibit the researchers offer a plot of voltage versus current the voltage flatlining at 0 volt as expected in Ohm's law (V = I * R) when the resistance is zero as per claim. The material is described as resembling lead apatite (Pb5(PO4)3OH). In one source this material gets mentioned as forming when phosphates are added to drinking water to prevent lead from leaking from lead pipes. The article explains that although in both materials de cells are hexagonal, those in the new material are shrunk by 0,48% on account of copper ions being smaller than lead ions. According to the article this makes all the difference: most materials with high superconductivity to date for example sulfur hydride rely on high pressure to force the same cell collapse. The authors also involve the notion of quantum wells, layers between atoms where electrons are confined and only have discrete quantum energy levels. In the material a quantum well is supposed to exist between lead and oxygen atoms.

The researchers to not really explain how they arrived at the novel material. You do not just decide to throw copper at lanarkite. The article suggests the formulation has been around as an ceramic (Korean 1986 article referenced). The super conductance of elemental lead has been known for over a 100 years (below 10K) and perhaps if you decide you need additional copper and a hexagonal lattice, then lead apatite comes into view. The article has been published on ArXiv and therefore not peer-reviewed. Curiously ArXiv also has a second article with same authors and pretty much the same content here. The acknowledgments mention over 20 years knowledge accumulation supported by various Korean research grants.