Source | Heart of the Machine
While scientists all over the world are scrambling to do experiments, some people have provided theoretical support for the recent Korean scientific research team's research on "normal temperature and pressure superconductivity".
A few hours ago, the Lawrence Berkeley National Laboratory (LBNL) submitted a paper on arXiv with results supporting LK-99 as a room temperature ambient pressure superconductor .
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At present, the paper has attracted extensive attention and discussion on Twitter.
Some people read the paper for the first time and said: This is a major discovery. The speed of research submission is extremely fast, but the thinking in it is careful enough.
In the study, LBNL nanostructured materials theory researcher Sinéad Griffin, using computing capabilities at the U.S. Department of Energy to run simulations, says he has found a theoretical basis for superconductivity in copper-doped lead apatite, an isolated flat band at the Fermi level is a sign of a superconducting crystal.
Through computer models, we have theoretically described what properties the material should have if room-temperature superconductivity exists in the real world. The LK-99, which is now attracting global attention, has this special property.
This may also be the first related research to prove the feasibility of the "normal temperature and pressure superconductor" theory.
After the paper was submitted, the author immediately tweeted: The paper has been dropped, you can sleep for a while.
The title of the thesis is "Origin of correlated isolated flat bands in copper-substituted lead phosphate apatite".
Method overview
All density functional theory (DFT) calculations were performed using the Vienna Ab initio Simulation Package (VASP), a software package for quantum mechanical calculations. Considering the low localization of Cu-d states, a Hubbard-U correction was experimentally applied. U values between 2 eV and 6 eV were also tested experimentally and found to be similar to all calculated values. The results in the main text are for U = 4 eV, which gives lattice parameters within 1% of the experimental results.
Figure 1 below. (a) is the lead apatite structure, as described in the main text, with two unequal lead sites. The O or OH columns are located in the central column defined by the Pb(2) hexagonal structure. Calculated electron position function of Pb_10(PO_4)_6OH_2. Oxygen radicals around Pb(2) are repelled by lone pairs.
▲Figure 1
The lead apatite structure in Figure 2(a) below shows nine coordinated Pb (1) sites. b) Cu substitution structure showing hexacoordinated Cu and Pb (1) sites with distorted triangular prism coordination, two different bond lengths, and a rigid twist of 24 ◦ between the upper and lower triangles. On the right is the crystal field diagram of Cu-d 9 .
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Figure 3 below shows the calculated spin-polarized electronic band structure (left) and the corresponding density of states. The orange solid line on the left of the figure represents the spin-up energy band, and the blue dashed line represents the spin-down energy band. The gray shading on the right of the figure indicates the total density of states, where the Cu-d track is shown in pink and the adjacent Op track is shown in green. In both plots, the Fermi level is set to 0 eV.
▲Figure 3
Notably, the study found a set of isolated planar bands across the Fermi level with a maximum bandwidth of ~130 meV (see Figure 4 above):
These theoretical results suggest that the apatite structure provides a unique framework for stabilizing highly localized Cu-d^9 states that form strongly correlated flat bands at the Fermi level. The central role of the stereochemically active 6s^2 lone electron in Pb(2) is manifested in the formation of chiral charge density waves and the propagation of structural distortions connecting the polyhedra.
When Cu is substituted on the Pb(1) site, the result is a cascade of structural changes, including lattice parameter reduction, coordination changes, and polyhedral tilt changes, leading to localized Jahn-Teller twisted triangular prisms around Cu. The result is a set of flat, abnormal, half-filled isolated d_yz/d_xz bands.
write at the end
Previously, people continued to doubt the credibility of high-temperature superconductivity, and laboratories in many countries expressed failure to reproduce it. Recently, Beihang University and the Shenyang National Laboratory for Materials Science of the Chinese Academy of Sciences both expressed unsatisfactory results in their papers on the reproduction of LK-99. The Korean team re-uploaded their paper on arXiv.
And the latest news has given us hope again.
At least the Berkeley Lab that submitted the paper is not an ordinary institution.
Lawrence Berkeley National Laboratory (LBNL), or Berkeley Lab for short, is a multidisciplinary research facility operated by the University of California system for the U.S. Department of Energy (DOE). Its main research scope includes basic energy science, biological and environmental system science, advanced scientific computing, basic properties of matter, future accelerators, sustainable energy technologies, etc.
From the 1950s to the present, Berkeley Lab has been one of the international physics research centers, and a total of 12 researchers related to Berkeley Lab have won the Nobel Prize.
The sole author of the new study, Sinéad Griffin, is currently a Researcher in Theory of Nanostructured Materials at LBNL, where she received her PhD at ETH Zurich in 2014.
Her research focuses on combining analytical and computational methods to understand, manipulate and design the functional properties of quantum materials, including magnetism, multiferroics and topological order, with applications ranging from quantum information science to next-generation microelectronics. In addition, she is particularly interested in the intersection between condensed matter science and high energy physics.
As people's understanding of materials such as LK-99 gradually becomes clear, we may be able to find a way to verify room temperature superconducting substances more quickly.
