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Ferromagnetic half levitation of LK-99-like synthetic samples

339 点作者 platz将近 2 年前

19 条评论

versteegen将近 2 年前
Very interesting comments on the paper by Prof. Michael S. Fuhrer <a href="https:&#x2F;&#x2F;nitter.net&#x2F;i&#x2F;status&#x2F;1688755932275384320" rel="nofollow noreferrer">https:&#x2F;&#x2F;nitter.net&#x2F;i&#x2F;status&#x2F;1688755932275384320</a><p>&gt; But I think they buried the lede a little. Ferromagnetism is novel and unexpected in this material system, and might be interesting. But strong diamagnetism even more so<p>&gt; Even if the diamagnetic fraction is the entire sample (appears less) then it would be the second-strongest diamagnet known (and pyrolytic graphite&#x27;s diamagnetism is very anisotropic). In both Bi and graphite, diamagnetism results from unusual band topology. It&#x27;s not common<p>&gt; Overall, some evidence that as-synthesized nominally Pb_10-xCu_x(PO4)O (&quot;LK-99&quot;) is magnetically quite unusual, with different fractions showing soft ferromagnetism and strong diamagnetism
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VHRanger将近 2 年前
After reading the r&#x2F;physics thread on LK-99 [1] I&#x27;ve cooled significantly on the matter.<p>Basically: people who work in SC think the initial science seems very sloppy and the replication attempts don&#x27;t come close to what you need to demonstrate a RT SC<p>[1] <a href="https:&#x2F;&#x2F;www.reddit.com&#x2F;r&#x2F;Physics&#x2F;comments&#x2F;15i3h9d&#x2F;lk99_megathread&#x2F;jus73e6&#x2F;" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.reddit.com&#x2F;r&#x2F;Physics&#x2F;comments&#x2F;15i3h9d&#x2F;lk99_megat...</a>
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hliyan将近 2 年前
According to this: <a href="https:&#x2F;&#x2F;twitter.com&#x2F;Andercot&#x2F;status&#x2F;1688598313497694208" rel="nofollow noreferrer">https:&#x2F;&#x2F;twitter.com&#x2F;Andercot&#x2F;status&#x2F;1688598313497694208</a><p>&quot;...there is a less well-known exception to this rule called Brauenbecker extension which provides a mathematical proof that levitation is possible with a simple diamagnetic in a dipole field so long as the diamagnetic material mass is very small relative to the strength of the magnetic field.&quot;<p>I was very hopeful in the early days and was following the developments eagerly. Unfortunately, now I&#x27;m 99% convinced that LK99 is not a superconductor. Hopefully, what we learned from the saga and the momentum will help advanced the field a bit faster.
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rishav_sharan将近 2 年前
Naive question, and I hope someone more knowledgeable than me can enlighten me here;<p>Why are we even testing for superconductivity with levitation, instead of just checking for current loss&#x2F;heat loss while conducting?
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p-e-w将近 2 年前
So if good old ferromagnetism&#x2F;diamagnetism is sufficient to explain the half-levitation shown in the video:<p><i>How can I build my own half-levitating objects from standard materials?</i><p>I&#x27;ve seen the science toys using pyrolytic carbon, but they are nowhere close to the effect from the video. Levitation height with pyrolytic carbon is like 1&#x2F;20th of what the video demonstrates. The disc in the video looks like it&#x27;s just about to take off. Can this be replicated with previously known materials at room temperature?
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sethammons将近 2 年前
&gt; We argue that, together with the pronounced shape anisotropy of the small fragments, the soft ferromagnetism is sufficient to explain the observed half levitation in strong vertical magnetic fields. Our measurements do not indicate the presence of the Meissner effect, nor zero resistance, in our samples, leading us to believe that our samples do not exhibit superconductivity.
JohnBooty将近 2 年前
What happened to the original LK-99 samples that (allegedly) displayed SC properties?<p>Were they just thrown in the dustbin, or what?<p>I haven&#x27;t seen that question answered or even asked anywhere, but I&#x27;m just a layman so maybe I&#x27;m not looking in the right places.
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scythe将近 2 年前
A ferromagnetic oxide featuring copper as the sole transition metal would be very weird. I&#x27;m not aware of any examples of the copper block demonstrating ferromagnetism without a more &quot;conventional&quot; ferromagnetic transition metal (from Cr to Ni and cousins).<p>But ferromagnetism has been demonstrated in black phosphorus:<p><a href="https:&#x2F;&#x2F;www.sciencedirect.com&#x2F;science&#x2F;article&#x2F;pii&#x2F;S0038109818303983" rel="nofollow noreferrer">https:&#x2F;&#x2F;www.sciencedirect.com&#x2F;science&#x2F;article&#x2F;pii&#x2F;S003810981...</a><p>So the most likely explanation for the observation here is that the sample contains black phosphorus. But do all the samples contain black phosphorus?
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freeone3000将近 2 年前
So a completely different compound in a completely different shape.
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arpowers将近 2 年前
My main concern: Where are the original authors and why are they not helping people synthesize the replications?
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m3kw9将近 2 年前
Has anyone even seen a ferromagnet stand up like that in a magnetic field?
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gfodor将近 2 年前
If your sample&#x27;s resistivity goes down as it warms up, odds are you didn&#x27;t make the same thing the Koreans did.
lifthrasiir将近 2 年前
Since someone blamed &quot;Soviet fan fiction&quot; in which I did take a part (oops) [1], let&#x27;s make my opinions explicit. I&#x27;m very sure at the moment:<p>- That the publish of two arXiv papers was accidental and the second paper was only published to claim the proper authorship, thus the exact publish date was never controllable.<p>- That top-tier Chinese universities <i>do</i> use Bilibili to post early results. This makes very hard to dismiss all Bilibili videos, though probably most would be.<p>- That you can produce something like the floating rock as seen in the original videos with a synthesis method similar to the paper states.<p>- That the synthesis method has an extreme variability depending on parameters. No single reproduced LK-99 samples are same.<p>- Thus, that Q-Center did make something according to this synthesis method as well, but that is probably different to other reproduced samples.<p>I&#x27;m cautiously positive that:<p>- That LK-99 is not a deliberate fraud. The most probable possibility at the moment is therefore an honest but misguided mistake. I still reserve a nonzero but not large probability (5%) that this is indeed novel to superconductivity.<p>- That LK-99 indeed has some peculiar properties when synthesis parameters are controlled right. The large variability does suggest singularities in the middle and Q-Center might somehow have gotten the jackpot.<p>- That at least some authors (notably Hyun-Tak Kim) are clearly distinguishing the superconductivity and superconductor [2]. In the other words, they are aware that LK-99 (supposedly) exhibits superconductivity but might not be considered as a superconductor.<p>- That there is a Russian group of scientists that claim some relevant knowledge and feel uneasy about the apparent dismissal of it. This might be the most controversial point I like to make, and my relative confidence partly comes from private information (like, I have verified the credential of Iris privately) so you don&#x27;t have to completely trust me on this.<p>- That the research group has not settled on a single theoretical explanation. This is probably why all LK-99 papers were different from each other in theory, and also why Young-Wan Kwon became &quot;disgruntled&quot; as Hyun-Tak Kim might have been his substitute.<p>- That the late professor Tong-Seek Chair is indeed a madman, regardless of the veracity of his theory.<p>I have suspicions that:<p>- That the paper is intentionally vague about the synthesis method. This method is notably different from what their international patent describes, and this is AFAIK typical in the material science. Probably the paper describes a low-yield and low-quality but easy method, and their trade secret is an efficient process.<p>- That Russian scientists and possibly LK-99 folks do have some theory that describes LK-99 better. I had to slightly weaken this point in the previous article because the actual difference was very unclear to me and other proofreaders (we have discovered this during the rewrite to avoid apparent misreadings). I now suspect that there is no actual theoretical difference but different paradigms may have resulted in different blindspots. So the &quot;acceptance&quot; of theory without paradigm may be seen as the fake acceptance to them, possibly explaining their sentiments.<p>- That China realized this possibility as well and wanted to maximize their leverage, explaining why China universities go crazy about this.<p>- Therefore, under these assumptions, that Q-Center&#x27;s apparently suspicious behavior can be fully explained.<p>I believe all of them needed me no advanced physics knowledge to derive. Any questions about those points are welcomed.<p>[1] See the original reply <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=36996337">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=36996337</a> and the current version <a href="https:&#x2F;&#x2F;hackmd.io&#x2F;@lifthrasiir&#x2F;lk-99-prehistory" rel="nofollow noreferrer">https:&#x2F;&#x2F;hackmd.io&#x2F;@lifthrasiir&#x2F;lk-99-prehistory</a> for the context.<p>[2] <a href="https:&#x2F;&#x2F;hackmd.io&#x2F;@sanxiyn&#x2F;seize-interview" rel="nofollow noreferrer">https:&#x2F;&#x2F;hackmd.io&#x2F;@sanxiyn&#x2F;seize-interview</a>
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rcpt将近 2 年前
Does that PDF have a video embedded?
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Forgotthepass8将近 2 年前
Why hasn&#x27;t the west published anything on this?
jonathan_oberg将近 2 年前
Ah damn.
kewp将近 2 年前
Someone on YouTube mentioned that LK99 is ceramic ie not metal which nullifies many of its potential uses even if it does turn out to be superconducting
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lamontcg将近 2 年前
I thought LK-99 looked like bullshit from the start, but the conclusions of this preprint should really be confirmed and there&#x27;s still a lot they don&#x27;t understand about the behavior of the sample that should get more fully explained. And there might be something with this material showing semiconductor like behavior that could still prove more mundanely useful.
ldjkfkdsjnv将近 2 年前
I knew it was fake, there would have been a huge rise in the stock market. Financial markets would have sniffed this out. The market never lies. If anything, this was an obvious opportunity to short it on prediction markets.
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