China Arxiv – First-principles study on the electronic structure of Pb10−xCux(PO4)6O (x=0, 1)
Junwen Lai,1, 2, ∗, Jiangxu Li,1, ∗ Peitao Liu,1, † Yan Sun,1, ‡ and Xing-Qiu Chen1
1Shenyang National Laboratory for Materials Science, Institute of Metal Research,
Chinese Academy of Sciences, 110016 Shenyang, China.
2School of Materials Science and Engineering, University of Science and Technology of China, 110016 Shenyang, China.
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 Pb10(PO4)6O 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.
We find that the doping effects of Au are more similar to Cu than those of Ag. This observation may be explained by the closer volumes between Au-doped and Cu-doped lead-apatites (see Table I). It is worth mentioning that, compared to Cu, Au doping further narrows the two flat bands, brings the VHS1 at the M point and VHS3 at the L point closer to the Fermi level, and results in larger DOSs around the Fermi level. These results suggest that Au-doped lead apatite may also exhibit similar superconducting properties as the Cu-doped one.
China First Principles Analysis
In conclusion, we have performed a thorough firstprinciples electronic structure analysis of both LK-99 and its parent compound. Our results demonstrate that the parent compound without doping is an insulator with a large band gap. Cu doping closes the band gap, resulting in an insulatormetal transition and volume contraction. The band structures of LK-99 exhibit novel characteristics around the Fermi level, which are manifested by the presence of a half-filled flat band and a fully-occupied flat band with two VHSs each. These two flat bands arise from both the 2p orbitals of 1/4-occupied O2 atoms and the hybridization of the 3d orbitals of Cu with the 2p orbitals of its nearest-neighboring O1 atoms, necessitating a minimal two-band low-energy effective model. The former 2p orbitals of 1/4-occupied O2 atoms lead to a one imensional-like cylindrical conduction channel along the c axis surrounded by insulating PO4 units, whereas the latter hybridized Cu-3d orbitals and O1-2p orbitals give rise to a twodimensional-like electron charge distribution in the ab-plane. The observed VHSs are robust against electronic correlation effects and their band energies can be tuned by doping different elements. We find that Au exhibits doping effects more similar to Cu than Ag. We anticipate that the distinctive electronic structures of LK-99 that we observed in this study will aid in identifying the source of its exceptional superconducting properties.
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It’s interesting that Iris suggested looking at uranium too…
Huazhong University of Science and Technology was successful.
You may be surprised to see the whole paper is in English (well, a moment to consider mere pdf reader accommodation) and says as much as that all things being the same, gold would do as well. That’s handy enough a tip, given that the canny thing to do is set up worker safety at a mine that nearly drills in such a mineral (dumps tailings…ok) and start making samples so the nice Cu substitution for Pb is likelier and test for conductivity and the Meissner Effect. This gives a bit of a sanity test if not the thermodynamic annealing workup side…
Extremely confounding situation. We’ve got this flicker of an interesting electrical property in some samples and models that suggest the substitution of 10% Cu needs to be in a specific crystal location without a clear way to park it there with laboratory chemistry.
You’ve got Argonne with a severe critique:
“They come off as real amateurs… They don’t know much about superconductivity”
And US national labs with whiz bang models using unfamiliar terms like “fermi surface” and other quantum jargon. Can’t trust models though – they all have screwdrivers and are tuned (usually to align with funding).
I think the comment out Argonne was half-cocked – that guy may yet get egg on his face.
If Lawrence Berkeley and CNL see potential in the way the Cu substitution distorts the crystal, giving the flicker of interesting electrical properties, then I think we still have a wave of innovation coming – interesting graduate studies at least.
I’m always happy to see the national labs actually make contact (hit the ball) since they strike out fantastically while continually rehashing alt-fission concepts.
So the China National Lab is saying that yes, LK-99 does have some degree of superconductor abilities?
No, they’re saying that IF LK-99 is a superconductor, replacing the copper with gold would probably also result in a superconductor. And that there are indications the superconductivity is at least plausible.