Another Computational Analysis Paper Says LK99 Can Be a Superconductor and Modification Will Make It Better

Computational theorists believe that the LK99 structure is promising and have discovered ways to improve LK99’s structure. The researchers think it is essential to gain a deeper understanding of the relationships between the LK-99 structure and properties, which could further open up new avenues for even high-temperature superconductivity (HTS). LK-99 was reported to have Tc as high as 400 K (127 ◦C) at ambient pressure. The replication of the LK99 experimental findings and the discovery of similar materials would revolutionize the field of superconductivity and open a wide range of next-generation technological applications, including but not limited to superconducting quantum interference devices (SQIDs), energy transmission systems, levitating trains, superconducting transistors, single-photon detection, quantum sensing, and quantum computing devices.

The s-wave pairing has been proposed for the possible HTS in LK-99. The specific arrangements of atoms with types of orbitals symmetry can, however, lead to either the s-wave or d-wave pairing mechanism. Further research is crucial to investigate and understand the complex structure property relationships in LK-99 compounds.

While the mechanism behind the potential room temperature superconductivity of LK-99 is unknown, it is argued that the long-range electron-phonon (e-ph) interactions cannot play an important role in inducing such phenomenon. Note, however, that there is no sufficient evidence yet for short-range e-ph interactions. Regardless of the range of e-ph interactions, the materials should possess the high electronic density of states (DOS) at the Fermi level in order to exhibit superconductivity. The flat band with a narrow bandwidth of 0.06 eV in the band structure of the lower-energy configuration of Pb9Cu(PO4)6O with one Cu substitution on a Pb(2a) site, indeed suggests that the LK-99 with such Cu arrangement might have higher DOS at the Fermi level. In the case of two Cu substitutions in the lower-energy configuration, the existence of a flat band around BZ center can lead to higher DOS than the other band which has a relatively larger bandwidth around the same region. Taking these electronic factors together with structural distortion into consideration, there might be a similar mechanism of phonon mediated long-range interactions as seen in other high-temperature superconductors, possibly with enhanced e-ph interactions in LK-99 compounds. Thus, it implies a need for a sophisticated quantum many-body theory to explain the potential quantum phases in LK-99. Due to the limitations of known physical models, the development of new techniques is critical.

Conclusions
Using the atom combinatorics-based approach within the supercell approximation and subsequently performing DFT+U optimization of 28 configurations (4 of (111) and 24 of (112) unit cells). Researchers found the most thermodynamically favorable structures of (1×1×2) Pb10−xCux(PO4)6O with x=1 where Cu atoms replace Pb(2a) and Pb(1b) sites, with Cu-Cu distance of 3.692 A. Moreover, the volume of Pb9Cu(PO4)6O is found to smaller than that of Pb10(PO4)6O, thus suggesting the existence of strain in Cu-substituted lead apatite compounds. Our DFT+U calculations indicate that the partially filled electronic state calculated at the BZ center is spatially localized around the Cu atom. In the case of the pristine Pb10(PO4)6O compound, for the Pb site they did not observe such spatial localization of the topmost occupied state. The calculated Fermi surface turns out to be a prolate-spheroid-like shape, and electrons in these regions are expected to couple with short/longrange phonons. From band structure calculations, they found an electron pocket around the BZ center. Upon suitable doping, one might enhance the electronic density of states at the Fermi level. For the low-energy configuration of single Cu substitution, one flat band has a more narrow bandwidth than the other, thus suggesting strong correlated physics in LK-99 compounds. The bands degeneracy at Γ and A high-symmetry points, as observed for higher-energy configuration with one Cu substitution, is not found to exist at the same high-symmetry K-points when two Pb atoms are substituted by Cu atoms forming a local dimer in a distorted LK-99 structure.

Superconductivity, a fascinating quantum state of matter, at room temperature and ambient pressure can find many promising next-generation technological applications such as quantum sensing and quantum computing devices. The ability to enhance the superconducting transition temperature (Tc) by several state-of-the-art design techniques, including the structural modification in materials, has been a long sought-after goal in solid-state physics and materials science. Very recently, the experimental realization of potential room-temperature ambient-pressure superconductivity was reported for Cu-substituted lead apatite, Pb_{10-x}Cu_x(PO4)6O (x~0.9-1.0), so-called LK-99 material. Nonetheless, important questions remain unresolved, particularly, understanding how the arrangements of substituted Cu on Pb sites in the LK-99 structure would minimize system’s energy and might affect its electronic structure. We address these relevant questions by enumerating possible configurations of Cu in Pb_{10-x}Cu_x(PO4)6O at 10% Cu substitution and performing density functional theory with Hubbard U correction (DFT+U) calculations of structural and electronic properties of selected configurations. We find that for (1x1x2) supercell, the most energetically favorable substitution sites are the nearest Pb(1) and Pb(2). The partially filled electronic state calculated at the Brillouin zone center is spatially localized around the Cu atom. For the low-energy configuration of single Cu substitution, we find that one electronic band is very flat with a narrow bandwidth of 0.06 eV. The bands degeneracy at Γ and A high-symmetry points that is observed for a higher-energy configuration with one Cu substitution, disappears when two Cu atoms form a local dimer in a distorted LK-99 structure.