Reproduction First demonstration of superconductivity at room temperature and pressure!

Just as scientists around the world are scrambling to do experiments, someone has provided theoretical support for the recent ambient pressure superconductivity research by a team of South Korean researchers.

A day earlier, the Lawrence Berkeley National Laboratory (LBNL) in the United States submitted a paper on arXiv with results that support LK-99 as a room-temperature ambient pressure superconductor.

"Origin of correlated isolated flat bands in copper-substituted lead phosphate apatite."

The author of the paper is a theoretical nanostructured materials scientist and researcher in high energy physics and condensed matter at Lawrence Berkeley National Laboratory. Currently, she leads a research group located at Berkeley Lab's Materials Science Division and Molecular Foundry: the GriffinGroup.

The paper has now garnered a lot of attention and discussion on Twitter. Some people who have read the paper for the first time have said that it is a major discovery, and that the research was submitted very quickly, but with enough thought put into it.

The paper says, "A recent report on the room-temperature superconductivity of copper-substituted apatite (LK99) at atmospheric pressure has stimulated interest in what materials and mechanisms can achieve high-temperature superconductivity. Here, I perform density-functional theory calculations on copper-substituted lead-phosphate apatite, identifying the associated isolated flat band at the Fermi level - a common feature of high transition temperatures in the established family of superconductors. "

"I elucidate the origin of these isolated bands: namely, structural distortions induced by copper ions and chiral charge density waves from lead lone pairs. These results show that a minimal two-band model can cover most of the low-energy physics in the system. Finally, I will discuss the implications of my findings for possible superconductivity in copper-doped apatite."

This means that Sinéad Griffin's simulations, using the computational power of the U.S. Department of Energy, have found a theoretical basis for the superconductivity of copper-doped lead apatite: isolated flat bands at the Fermi energy level are the hallmark of superconducting crystals.

Through computer modeling, this article theoretically describes what the material should be if room-temperature superconductivity existed in the real world. LK-99, which is now attracting global attention, has this particular property.

"The calculations presented in this paper show that copper substitution at the appropriate (Pb(1)) site displays many of the key features of high TC superconductivity, namely an exceptionally flat isolated d-pop (d-manifold), as well as possible fluctuating magnetism, charge, and phonons. However, the substitution at another Pb(2) site does not appear to have these sought-after properties, even though it is the lower energy substitution site. This result suggests that it is a synthetic challenge to obtain bulk superconducting samples with copper substitutions at the appropriate sites. Nevertheless, given these tantalizing theoretical features and experimental reports of potentially high TC superconductivity, I expect that the discovery of this new class of materials will spur further research on doped apatite minerals."

This may also be the first time in related research that the theoretical feasibility of an ambient temperature and pressure superconductor has been successfully demonstrated.

Specifically, this experiment performed all density-functional theory (DFT) calculations using the Vienna Ab initio Simulation Package (VASP), a software package for quantum mechanical calculations. The experiment applied the Hubbard-U correction to account for the low localization of Cu-d states. The experiment was also tested for values of U between 2 eV and 6 eV, and it was found that the experimental results were similar to the results for all calculated values.

The results in the original paper are for U = 4 eV, which gives a lattice parameter that differs from the experimental results by 1%.

(a) Apatite Pb structure with two unequal Pb sites as described in the main text. the O or OH columns are located in the central column defined by the Pb(2) hexagonal structure. (b) Calculated electron localization function for Pb10(PO4)6OH2. oxygen roots around Pb(2) are repelled by the lone pair.

(a) Apatite lead structure showing nine coordinated Pb(1) sites. (b) Cu-substituted structure showing six-coordinated Cu and Pb(1) sites with twisted trigonal coordination, with two different bond lengths that are rigidly twisted 24◦ between the upper and lower triangles. The crystal field diagram of Cu-d9 is shown on the right.

The calculated spin-polarized electronic energy band structure (left) and the corresponding density of states (right). Solid orange lines indicate the spin-up bands and dashed blue lines indicate the spin-down bands. The total density of states is shaded in gray and shows the projection of the Cu-d orbital (pink) and its neighboring O-p orbital (green). In both panels, the Fermi level is set to 0 eV and is marked with a dashed line.

Calculated energy band structure of spin-polarized electrons in a smaller energy range near the Fermi level, showing isolated two-band Cu-d manifolds. The Fermi level is set to 0 eV and is marked with a dashed line.

Notably, this study finds a set of isolated planar bands across the Fermi energy level with a maximum bandwidth of ~130 meV:

In response to these theoretical results, the authors show that the apatite structure provides a unique framework for stabilizing the highly localized Cu-d9 state, which forms strongly correlated flat bands at the Fermi energy level.Stereochemically active 6s2 lone electrons in Pb (2) The central role of the 6s2 lone electrons is manifested in the formation of the chiral charge-density wave and the propagation of structural distortions in the connected polyhedra.

There are two origins for the isolated flat bands in LK-99:

- One origin is due to the structural distortion of the material due to copper ions, i.e., a change in the atomic arrangement.

- The other origin is due to the formation of a special charge density wave by isolated electron pairs of lead ions.

The authors note that these results suggest a simplified model, the "two-band model," that better describes the low-energy physical behavior in this material. Overall, it turns out that the conduction paths of the electrons are in just the right conditions and locations to make them superconducting.

Previously, doubts persisted about the credibility of high-temperature superconductivity, with laboratories in several countries reporting failed reproductions. on July 31, researchers from Beihang submitted a paper on arXiv stating that the experimental results did not reveal the superconductivity of LK-99, and a paper from the National Laboratory of Materials Science at the Chinese Academy of Sciences (CAS) in Shenyang on the reproduction of LK-99 stated that the results were unsatisfactory.

The Korean team re-uploaded their paper on arXiv.

On July 29, the team submitted a revised second version of their paper, with substantial changes to only one figure.

This new proof of theory certainly raises hopes for a resurgence.

As events related to room-temperature superconductivity heat up, we believe that we will be able to find a way to verify room-temperature superconducting substances more quickly when the understanding of materials such as LK-99 becomes clearer.

Reference Links:

[1]https://arxiv.org/abs/2307.16892

[2]https://redian.news/wxnews/512931

[3]https://foundry.lbl.gov/about/staff/sinead-griffin/

[4]https://sineadgriffin.com/

[5]https://www.reddit.com/r/Futurology/comments/15f1axs/berkley_material_sciences_corroborate_room/

[6]https://arxiv.org/ftp/arxiv/papers/2307/2307.16802.pdf

[7]https://arxiv.org/pdf/2307.16040.pdf

[8]https://www.ithome.com/0/709/541.htm