https://arxiv.org/abs/2308.00698


https://arxiv.org/abs/2308.00698

Pb-apatite framework as a generator of novel flat-band CuO based physics, including possible room temperature superconductivityHere, based upon density functional theory (DFT) calculations, we present the basic electronic structure of CuPb9(PO4)6O (Cu-doped lead apatite), showing that the low energy (near-Fermilevel) states are dominated by Cu-O hybrid states. The filling of these states is nominally d$^{9}$, consistent with the standard Cu$^{2+}$ valence state. We find these states to be unusually flat (~ 0.2 eV dispersion), giving a very high density of electronic states (DOS) at the Fermi level that we argue can be a host for novel electronic physics, including potentially room temperature superconductivity. The states are in general sensitive to symmetry-lowering gapping possibilities that would remove the spectral weight from EF, but could be protected from this by disorder/doping heterogeneity in a real material. Importantly, this disorder is expected to be less damaging to superconductivity. Further, we claim that the emergence of these flat bands should be due to weak wavefunction overlap between the orbitals on Cu and O sites, owing to to the directional character of the constituent orbitals. Therefore, finding an appropriate host structure for minimizing hybridization between Cu and O while allowing them to still weakly interact should be a promising route for generating flat bands at EF and very high temperature superconductivity, regardless of whether LK-99 is such a realization.arxiv.org


Here, based upon density functional theory (DFT) calculations, we present the basic electronic structure of CuPb9(PO4)6O (Cu-doped lead apatite), showing that the low energy (near-Fermilevel) states are dominated by Cu-O hybrid states. The filling of these states is nominally d

9, consistent with the standard Cu2+valence state. We find these states to be unusually flat (~ 0.2 eV dispersion), giving a very high density of electronic states (DOS) at the Fermi level that we argue can be a host for novel electronic physics, including potentially room temperature superconductivity. The states are in general sensitive to symmetry-lowering gapping possibilities that would remove the spectral weight from EF, but could be protected from this by disorder/doping heterogeneity in a real material. Importantly, this disorder is expected to be less damaging to superconductivity. Further, we claim that the emergence of these flat bands should be due to weak wavefunction overlap between the orbitals on Cu and O sites, owing to to the directional character of the constituent orbitals. Therefore, finding an appropriate host structure for minimizing hybridization between Cu and O while allowing them to still weakly interact should be a promising route for generating flat bands at EF and very high temperature superconductivity, regardless of whether LK-99 is such a realization.



https://arxiv.org/abs/2308.00676

Electronic structure of the putative room-temperature superconductor Pb$_9$Cu(PO$_4$)$_6$O

A recent paper [Lee {\em et al.}, J. Korean Cryt. Growth Cryst. Techn. {\bf 33}, 61 (2023)] provides some experimental indications that Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O with $x\approx 1$, coined LK-99, might be a room-temperature superconductor at ambient pressure. Our density-functional theory calculations show lattice parameters and a volume contraction with $x$ -- very similar to experiment. The DFT electronic structure shows Cu$^{2+}$ in a $3d^9$ configuration with two extremely flat Cu bands crossing the Fermi energy. This puts Pb$_{9}$Cu(PO$_4$)$_6$O in an ultra-correlated regime and suggests that, without doping, it is a Mott or charge transfer insulator. If doped such an electronic structure might support flat-band superconductivity or an correlation-enhanced electron-phonon mechanism, whereas a diamagnet without superconductivity appears to be rather at odds with our results.

arxiv.org


A recent paper [Lee {\em et al.}, J. Korean Cryt. Growth Cryst. Techn. {\bf 33}, 61 (2023)] provides some experimental indications that Pb

10−xCux(PO4)6O with x≈1, coined LK-99, might be a room-temperature superconductor at ambient pressure. Our density-functional theory calculations show lattice parameters and a volume contraction with x -- very similar to experiment. The DFT electronic structure shows Cu2+ in a 3d9 configuration with two extremely flat Cu bands crossing the Fermi energy. This puts Pb9Cu(PO4)6O in an ultra-correlated regime and suggests that, without doping, it is a Mott or charge transfer insulator. If doped such an electronic structure might support flat-band superconductivity or an correlation-enhanced electron-phonon mechanism, whereas a diamagnet without superconductivity appears to be rather at odds with our results.

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