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#lk99

1 post1 participant0 posts today
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Quantum Observer

It’s Back: Researchers Say They’ve Replicated LK-99 Room Temperature Superconductor Experiment thequantuminsider.com/?p=23600 #Research #coppersubstituted_lead_apatite #CSLA #LK99 #roomtemperature_superconductor #Superconducting #superconductor #quantumdaily Insider Brief A team of researchers report the replication experiments suggest a copper-substituted lead apatite (CSLA) may serve as a candidate for room-temperature superconductivity. Last year, replication efforts on a similar r

The Quantum Insider · It's Back: Researchers Say They've Replicated LK-99 Room Temperature Superconductor ExperimentResearchers say a copper-substituted lead apatite (CSLA) may serve as a candidate for room-temperature superconductivity.
Public
Howard Chu @ Symas

3 new pre-prints talk about #LK99 being a semiconductor. This one shows that there's still a few different potential products of the synthesis, and while the common copper-doped forms are definitely semiconductors, sulphur doping might still yield a superconductor arxiv.org/abs/2309.07928

arXiv.orgDeciphering the Enigma of Cu-Doped Lead Apatite (LK-99): Structural Insights, Electronic Properties, and Implications for Ambient-Pressure SuperconductivityThe most recent discovery, the Cu-doped lead apatite LK-99, is a proposed room-temperature superconductor operating under ambient pressure. However, this discovery has brought a slew of conflicting results from different scientific groups. While some observed the absence of electrical resistance, others could not confirm any signs of superconductivity in LK-99. Here, we investigate the structural and electronic properties of LK-99 and its antecedent compounds through quantum mechanics (QM) and QM-based molecular dynamics (QM-MD) simulations. Our study elucidates the insulating nature of base compounds, Pb$_{10}$(PO$_4$)$_6$O and Pb$_{10}$(PO$_4$)$_6$(OH)$_2$, spotlighting their large band gaps. Notably, Cu doping in LK-99 disrupts its symmetry, yielding a distorted ground-state crystal structure with a triclinic P1 symmetry and CuO$_4$ square coordination. Such alterations predispose LK-99 to exhibit semiconducting behaviors, characterized by a flat band above the Fermi energy, arising from Cu-3d and O-2p orbitals. In addition, the S doping sustains the triclinic P1 symmetry but leads to a significantly reduced band gap, with a band emerging primarily from Cu-3d and S-3p orbitals. These findings are important in understanding LK-99's structural and electronic properties and provide a strategic compass for the development of high-T$_C$ superconductors.
Public
Scienza in rete :mastodon:

Due articoli apparsi sulla piattaforma di preprint arxiv.org hanno prospettato la scoperta di un #superconduttore “da sogno”, cioè in grado di lavorare e temperatura e pressione ambiente, chiamato #LK99.

Purtroppo durante un tavola rotonda dedicata al tema e tenutasi a settembre nell'ambito della Conferenza Europea sulla Superconduttività Applicata, ha mostrato che LK99 non è altro che una bufala.

Ne parla Riccardo Lucentini -> scienzainrete.it/articolo/sogn

Scienza in reteIl sogno della superconduttività e il caso di LK99«Dove posizioneresti questi autori in una scala da “truffatori senza vergogna” a “scienziati troppo entusiasti”?» Questa è la domanda che David Larbalestier, professore di ingegneria meccanica alla Florida State University, si è visto recapitare da un collega insieme all’articolo che annunciava la scoperta di un materiale superconduttore a temperatura ambiente.
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rexi

@futurism
newscientist.com/article/23847

"…researchers then measured how much a millimetre-sized sample of #lk99 resisted electricity passing through it at different temperatures and found…resistivity fell sharply from a sizeable positive value at 105°C (221°F) down to nearly zero at 30°C (86°F)…researchers also tested the material’s response to a magnetic field…because #superconductors are known to expel them as part of a phenomenon called the Meissner effect.…it also had near zero resistance…"

New Scientist · Room-temperature superconductor 'breakthrough' met with scepticismBy Karmela Padavic-Callaghan
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NeurophysicsLab Albrecht Haase

Unfortunately, this should finally dampen the general excitement about room-temperature #superconductivity:

"We therefore rule out the presence of superconductivity in Pb9Cu(PO4)6O crystals..." (known al #lk99)

arxiv.org/abs/2308.06256

arXiv.orgSingle crystal synthesis, structure, and magnetism of Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$OThe recent claim of superconductivity above room temperature in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O with 0.9 < $x$ < 1 (referred to as LK-99) has sparked considerable interest. To minimize the influence of structural defects and impurity phases on the physical properties, we have synthesized phase-pure single crystals with $x \sim 1$. We find that the crystals are highly insulating and optically transparent. X-ray analysis reveals an uneven distribution of the substituted Cu throughout the sample. Temperature ($T$) dependent magnetization measurements for $ 2 \leq T \leq 800$ K reveal the diamagnetic response characteristic of a non-magnetic insulator, as well as a small ferromagnetic component, possibly originating from frustrated exchange interactions in Cu-rich clusters in the Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O structure. No anomalies indicative of phase transitions are observed. We therefore rule out the presence of superconductivity in Pb$_{9}$Cu(PO$_4$)$_6$O crystals, and provide some considerations on the origin of anomalies previously reported in experiments on polycrystalline specimen.
Public
Ichinin :verified: :verified_paw: ✅🎯🙄

The supposed superconductor #LK99 is met with some scepticism as researchers elsewhere fail to confirm the Korean discovery: "The most credible attempts have found that LK-99—the name the Korean researchers gave the material—is not actually superconductive at room temperatures".

time.com/6301391/experts-skept

TimeWhy Experts Are Skeptical About That Supposed Superconductor BreakthroughBy Will Henshall
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Todd Knarr

The looks like a bust. It may be something, but it's looking like it's not a superconductor of any sort. Nobody can replicate it at all. If they really had a superconductor that nobody could reproduce, rather than file patents they'd take the route Heinlein's Shipstone took: lock down the few people who know how to do it so tight they'll never want to leave, then set up shop and start producing the stuff. Nobody will care how it works, as long as it works.

Public
KilleansRow 🇺🇲 🇺🇦🍀

Friday #LK99 and #Superconductivity Update:  #arXiv submissions for LK-99 now at 42. Find myself pulled towards more exploratory simulation work which has been goosed by the fact that #LK99 is thus far wholly uncooperative in demonstrating ambient superconductivity yet is revealing some unusual properties:

Multiple Slater determinants and strong spin-fluctuations as key ingredients of the electronic structure of electron- and hole-doped Pb10−xCux(PO4)6O

arxiv.org/abs/2308.09900

arXiv.orgMultiple Slater determinants and strong spin-fluctuations as key ingredients of the electronic structure of electron- and hole-doped Pb$_{10-x}$Cu$_x$(PO4)$_6$OLK-99, with chemical formula Pb$_{10-x}$Cu$_x$(PO4)$_6$O, was recently reported to be a room-temperature superconductor. While this claim has met with little support in a flurry of ensuing work, a variety of calculations (mostly based on density-functional theory) have demonstrated that the system possesses some unusual characteristics in the electronic structure, in particular flat bands. We have established previously that within DFT, the system is insulating with many characteristics resembling the classic cuprates, provided the structure is not constrained to the $P$3(143) symmetry nominally assigned to it. Here we describe the basic electronic structure of LK-99 within self-consistent many-body perturbative approach, quasiparticle self-consistent GW (QSGW) approximation and their diagrammatic extensions. QSGW predicts that pristine LK-99 is indeed a Mott/charge transfer insulator, with a bandgap gap in excess of 3eV, whether or not constrained to the $P$3(143) symmetry. The highest valence bands occur as a pair, and look similar to DFT bands. The lowest conduction band is an almost dispersionless state of largely Cu $d$ character. When Pb$_9$Cu(PO$_4$)$_6$O} is hole-doped, the valence bands modify only slightly, and a hole pocket appears. However, two solutions emerge: a high-moment solution with the Cu local moment aligned parallel to neighbors, and a low-moment solution with Cu aligned antiparallel to its environment. In the electron-doped case the conduction band structure changes significantly: states of mostly Pb character merge with the formerly dispersionless Cu $d$ state, and high-spin and low spin solutions once again appear. Thus we conclude that with suitable doping, the ground state of the system is not adequately described by a band picture, and that strong correlations are likely.
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