Lawrence Berkeley National Lab simulated this using heavy-duty compute power from the Department of Energy, and looked to see what would happen to the ‘electronic structure’ of this material, meaning, what are the available conduction pathways in the material. It turns out that there are conduction pathways for electrons that are in just the right conditions and places that would enable them to ‘superconduct’. More specifically, they were close to the ‘Fermi Surface’ which is like the sea-level of electrical energy, as in ‘0 ft above sea-level.’
National Lab (LBNL) results support LK-99 as a room-temperature ambient-pressure superconductor.
Simulations published 1 hour ago on arxiv support LK-99 as the holy grail of modern material science and applied physics.
Here’s the plain-english… pic.twitter.com/mQNQuO4TFu
— Andrew Cote (@Andercot) August 1, 2023
Sinead M. Griffin1,2
1Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA and
2Molecular Foundry Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
– The simulations modeled what the original Korean authors proposed was happening to their material – where copper atoms were percolating into a crystal structure and replacing lead atoms, causing the crystal to strain slightly and contract by 0.5%. This unique structure was proposed to allow this amazing property.
from Lawrence Berkeley National Lab simulated this using heavy-duty compute power from the Department of Energy, and looked to see what would happen to the ‘electronic structure’ of this material, meaning, what are the available conduction pathways in the material.
– It turns out that there are conduction pathways for electrons that are in just the right conditions and places that would enable them to ‘superconduct’. More specifically, they were close to the ‘Fermi Surface’ which is like the sea-level of electrical energy, as in ‘0 ft above sea-level.’ It’s believed currently that the more conduction pathways close to the Fermi surface, the higher the temperature you can superconduct at (An analogy might be how its easier for planes to fly close to the surface of the ocean due to the ‘ground effect’ that gives them more lift.)
– Lastly, these interesting conduction pathways only form when the copper atom percolates into the less likely location in the crystal lattice, or the ‘higher energy’ binding site. This means the material would be difficult to synthesize since only a small fraction of crystal gets its copper in just the right location.
These theoretical results suggest that the apatite structure provides a unique framework for stabilizing highly localized Cu-d states that form a strongly correlated flat band at the Fermi level. The central role of stereochemically active 6s2 lone pairs of Pb(2) manifests in the formation of a chiral charge density wave and the propagation of structural distortions with connected polyhedra.
When Cu is substituted on a Pb(1) site, the result is a cascade of structural alterations, including reduced lattice parameters, changes in coordination, and modified polyhedral tilts, leading to a local Jahn-Teller distorted trigonal prism around Cu. This results in an unusually flat set of isolated dyz/dxz bands with half-filling. I briefly note that achieving such a crystal field environment should also be possible in intercalated twisted heterogeneous bilayers where selection of different heterobilayers can provide the mirror symmetry breaking, while moir´e twist can provide an arbitrary rotation of the upper and lower triangles. In fact such a platform would be ideal for probing the physics found here given its broad
range of tunability and the state-of-the-art characterization probes for their interrogation.
In this system, I have identified several potential sources of fluctuations that could contribute to pairing. Firstly, I identified a charge density wave (CDW) driven by chiral lone pair ordering on the Pb(2) sites – the presence of this CDW is strongly connected to the structural rearragement that occurs when Cu is incorporated into the Pb(1) lattice sites. In addition to this, I identified two zone-center phonon modes that trigger the global structural deformation that occurs as a result of the Cu substitution, suggesting potentially strong electron-phonon coupling for these modes. Finally, I calculated the relative exchange interactions between Cu in neighboring unit cells. Interestingly for the out-of-plane coupling, that is, along the Cu-Pb-Cu one-dimensional chains, I find ferromagnetic coupling is favored by 2 meV/Cu over antiferromagnet coupling, even though the Cu are over 7 ˚A apart, suggesting that spin fluctuations could also play a key role.
Finally, the calculations presented here suggest that Cu substitution on the appropriate (Pb(1)) site displays many key characteristics for high-TC superconductivity, namely a particularly flat isolated d-manifold, and the potential presence of fluctuating magnetism, charge and phonons. However, substitution on the other Pb(2) does not appear to have such sought-after properties, despite being the lower-energy substitution site. This result hints to the synthesis challenge in obtaining Cu substituted on the appropriate site for obtaining a bulk superconducting sample. Nevertheless, I expect the identification of this new material class to spur on further investigations of doped apatite minerals given these tantalizing theoretical signatures and experimental reports of possible high-TC superconductivity.
This is an attempt of a more coherent thread of why, imo, yesterday’s prediction of a flat band at the Fermi level in #LK99 does not “bring us back” or does resolve the controversy. In short, the prediction assumes the proposed crystal structure is correct, but it might not be.
— Schoop Lab (@SchoopLab) August 1, 2023
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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