In a recent study by Lee et al., published in the Journal of Korean Crystal Growth and Crystal Technology, some interesting findings suggest that Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O, also known as LK-99, could potentially be a room-temperature superconductor at normal atmospheric pressure. The authors conducted density-functional theory calculations, which revealed similar lattice parameters and a volume contraction with varying levels of Cu. The electronic structure analysis showed that Cu$^{2+}$ occupied a $3d^9$ configuration, with two remarkably flat Cu bands intersecting the Fermi energy. This implies that Pb$_{9}$Cu(PO$_4$)$_6$O exists in a highly correlated state and is likely a Mott or charge transfer insulator without any doping. However, doping could potentially induce flat-band superconductivity or an electron-phonon mechanism enhanced by correlations. These findings contradict the expectation of Pb$_{9}$Cu(PO$_4$)$_6$O being a diamagnet without any superconductivity.
https://arxiv.org/abs/2308.00676