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I’m not an expert, but I’ve used superconductors (I believe YBCO) when I taught physics lab. We cooled samples down with liquid nitrogen and put them over a mag

by alecst 3y ago

I’m not an expert, but I’ve used superconductors (I believe YBCO) when I taught physics lab. We cooled samples down with liquid nitrogen and put them over a magnet. They levitate, but not like in the video that the Korean team released. True superconductors enjoy “flux pinning”, meaning wherever you put them on a magnet, they’ll freeze in that position (or move around an axis of constant flux.) In the LK-99 video that they released, they show that the sample is repelled by a magnet. This seems to contradict the HTS claim and wondered if I’m missing something because surely so many experts can’t be this wrong. My background is in physics, but not superconductors.

dawnofdusk 3y ago
Type-II super conductors may exhibit "flux pinning". Type-I super conductors do not.
- alecst 3y ago
  Cool thanks. Gonna read up a little on that. Edit: yea it's interesting. Believe it or not, I studied L-G theory in grad school, taught a lab about (type-II) superconductors, but had no idea that type-I superconductors didn't flux pin. Just leaving this here from Wikipedia: > The superconductor must be a type-II superconductor because type-I superconductors cannot be penetrated by magnetic fields. Some type-I superconductors can experience the effects of flux pinning if they are thin enough. If the material's thickness is comparable to the London penetration depth, the magnetic field can pass through the material. https://en.wikipedia.org/wiki/Flux_pinning https://en.wikipedia.org/wiki/Flux_pinning
  - adastra22 3y ago
    Also to follow up on your original point, this is a purported example of a linear superconductor. There are parallel columnar lines of superconductivity inside the mineral, like a bundle of wires. No such thing has ever been demonstrated before, and it is unlikely to have macro properties like those you are familiar with. For example, flux pinning is (IIRC) due to circular currents induced in the superconductor. But how do you induce a circular current into a straight-line conductive wire with ~zero cross section?
  - someplaceguy 3y ago
    > If the material's thickness is comparable to the London penetration depth, the magnetic field can pass through the material. Indeed. A girl I was seeing told me the same once, but obviously things didn't work out between us...
- zarzavat 3y ago
  As far as I understand it (not an expert on these things), flux pinning is caused by microscopic defects that allow the magnetic field to penetrate at certain points. An idealized superconductor that is perfectly uniform expels the magnetic field at all points and so would not display the effect, it would simply be diamagnetic. So it’s mistaken and somewhat perverse to view the absence of flux pinning as proof that something is not a superconductor. In the case of LK99, the claim is that it does not show flux pinning because the sample is impure and not uniformly superconductive, i.e. it is not expelling the magnetic field enough.
  - jamesmaniscalco 3y ago
    No defects needed for flux penetration in a type-II superconductor. When the conference length is smaller than the penetration depth (up to a factor of sqrt(2)), flux vortices can nucleate as soon as the surface magnetic field gets above the lower critical field Bc1.
    - jamesmaniscalco 3y ago
      Sorry, that should say “coherence length”.
  - jacquesm 3y ago
    That also explains - assuming it is all true - the lack of current through the sample.
- asdfman123 3y ago
  > Type-II super conductors may exhibit "flux pinning" Type-II diamagnetism?
- radioactivist 3y ago
  Even for type-II superconductors one may need single crystals if the material is anisotropic enough (e.g. if the flux pinning is confined mostly to 2D layers then randomly oriented grains in a powder aren't going to trap flux well)
cnhajzwgz 3y ago
Many experts are indeed questioning the apparent lack of flux pinning and wonder if it's just strong diamagnetism.
- m3kw9 3y ago
  I think it would be easy to recognize diamagnetism vs Superconducting and thus these superconducter experts wouldn’t embarrass themselves outing such papers
- lucubratory 3y ago
  I've already seen some videos/images from the lesbian Soviet hedge chemist and some other amateur/non-lab repro attempts showing that if it's diamagnetism, it's much, much stronger than pyrolitic graphite. At least 15x stronger. Diamagnetism also wouldn't explain the resistivity, critical temp, critical current, and critical field graphs. I think the realistic options at this point are: 1. Complete fraud, including opportunistic fraud by some online accounts who are faking partial replications. 2. Real superconductor of some kind, the papers are all fucked up because of the early leak by Kwon and internal Nobel jostling drama, and the production process is difficult, but fundamentally this is the real deal, RTAPS, but with a critical current and critical field that's lower than we would like, possibly (it's unclear what the measurements for these actually are). 3. They discovered a new type of material which is a very strong diamagnet, and then decided to fake the rest of a superconductor's properties because superconductivity is much more prestigious than a new powerful diamagnet. Replication efforts are having limited success with diamagnetism because it is actually diamagnetic.
  - whatshisface 3y ago
    There aren't any Soviet chemists...
    - lucubratory 3y ago
      Not everyone agrees, and therefore... https://youtu.be/oOV32P59-yI https://youtu.be/oOV32P59-yI
aqme28 3y ago
They claim that only a small part of that sample is superconducting, and that's why it shows that unusual behavior.

by alecst 3y ago

dawnofdusk 3y ago

Type-II super conductors may exhibit "flux pinning". Type-I super conductors do not.

alecst 3y ago
Cool thanks. Gonna read up a little on that. Edit: yea it's interesting. Believe it or not, I studied L-G theory in grad school, taught a lab about (type-II) superconductors, but had no idea that type-I superconductors didn't flux pin. Just leaving this here from Wikipedia: > The superconductor must be a type-II superconductor because type-I superconductors cannot be penetrated by magnetic fields. Some type-I superconductors can experience the effects of flux pinning if they are thin enough. If the material's thickness is comparable to the London penetration depth, the magnetic field can pass through the material. https://en.wikipedia.org/wiki/Flux_pinning https://en.wikipedia.org/wiki/Flux_pinning
- adastra22 3y ago
  Also to follow up on your original point, this is a purported example of a linear superconductor. There are parallel columnar lines of superconductivity inside the mineral, like a bundle of wires. No such thing has ever been demonstrated before, and it is unlikely to have macro properties like those you are familiar with. For example, flux pinning is (IIRC) due to circular currents induced in the superconductor. But how do you induce a circular current into a straight-line conductive wire with ~zero cross section?
- someplaceguy 3y ago
  > If the material's thickness is comparable to the London penetration depth, the magnetic field can pass through the material. Indeed. A girl I was seeing told me the same once, but obviously things didn't work out between us...
zarzavat 3y ago
As far as I understand it (not an expert on these things), flux pinning is caused by microscopic defects that allow the magnetic field to penetrate at certain points. An idealized superconductor that is perfectly uniform expels the magnetic field at all points and so would not display the effect, it would simply be diamagnetic. So it’s mistaken and somewhat perverse to view the absence of flux pinning as proof that something is not a superconductor. In the case of LK99, the claim is that it does not show flux pinning because the sample is impure and not uniformly superconductive, i.e. it is not expelling the magnetic field enough.
- jamesmaniscalco 3y ago
  No defects needed for flux penetration in a type-II superconductor. When the conference length is smaller than the penetration depth (up to a factor of sqrt(2)), flux vortices can nucleate as soon as the surface magnetic field gets above the lower critical field Bc1.
  - jamesmaniscalco 3y ago
    Sorry, that should say “coherence length”.
- jacquesm 3y ago
  That also explains - assuming it is all true - the lack of current through the sample.
asdfman123 3y ago
> Type-II super conductors may exhibit "flux pinning" Type-II diamagnetism?
radioactivist 3y ago
Even for type-II superconductors one may need single crystals if the material is anisotropic enough (e.g. if the flux pinning is confined mostly to 2D layers then randomly oriented grains in a powder aren't going to trap flux well)

cnhajzwgz 3y ago

Many experts are indeed questioning the apparent lack of flux pinning and wonder if it's just strong diamagnetism.

m3kw9 3y ago
I think it would be easy to recognize diamagnetism vs Superconducting and thus these superconducter experts wouldn’t embarrass themselves outing such papers
lucubratory 3y ago
I've already seen some videos/images from the lesbian Soviet hedge chemist and some other amateur/non-lab repro attempts showing that if it's diamagnetism, it's much, much stronger than pyrolitic graphite. At least 15x stronger. Diamagnetism also wouldn't explain the resistivity, critical temp, critical current, and critical field graphs. I think the realistic options at this point are: 1. Complete fraud, including opportunistic fraud by some online accounts who are faking partial replications. 2. Real superconductor of some kind, the papers are all fucked up because of the early leak by Kwon and internal Nobel jostling drama, and the production process is difficult, but fundamentally this is the real deal, RTAPS, but with a critical current and critical field that's lower than we would like, possibly (it's unclear what the measurements for these actually are). 3. They discovered a new type of material which is a very strong diamagnet, and then decided to fake the rest of a superconductor's properties because superconductivity is much more prestigious than a new powerful diamagnet. Replication efforts are having limited success with diamagnetism because it is actually diamagnetic.
- whatshisface 3y ago
  There aren't any Soviet chemists...
  - lucubratory 3y ago
    Not everyone agrees, and therefore... https://youtu.be/oOV32P59-yI https://youtu.be/oOV32P59-yI

aqme28 3y ago

They claim that only a small part of that sample is superconducting, and that's why it shows that unusual behavior.