Could be normal diamagnetism, or even ferromagnetism. Very hard to say as they don't even give any field strengths in the video, it's just a Neodym magnet they hold near the sample. If I understand the video correctly they just orient the magnet by hand, so I would not even rule out a ferromagnetic effect. There can be multiple regions with different orientation in such a polycristalline material, which can produce all kinds of weird effects. Not saying that it's not a superconductor, just that I would not draw any conclusions from this video. If this was a type-II superconductor and the flux pinning is strong enough to lift the flake up you should be able to drag it across the bottom of the beaker with the magnet as the magnetic flux lines "impale" the crystal, i.e. they are in an energy minimum and moving them out of there causes resistance as they need to break the superconductivity in the material surrounding the defect where they are pinned. If it's just diamagnetism that's not the case. So observing that the flake is completely stationary when the magnet is moved in our out tells me this likely isn't flux pinning we're seeing.
I'm a bit skeptical how they even know it's the right material, getting the doping right seemed quite intricate so it would seem quite extraordinary that they can hit the right process after trying for a few days. Not saying they didn't, but so far I'm rather inclined to believe they just got a ferromagnetic metal flake (which is easy to get following the thermal annealing process they did, or even by banging the material up a bit as they seem to have done for getting it out of the synthesis tubes).
To me, this video looks like the sample is experiencing a torque, not a force. (Or at least not a force that is sizable compared to the sample’s weight.). The sample is doing a remarkable job of cavorting without actually going anywhere. Magnetic dipoles experience a torque proportional to the applied field, whereas the force is proportional [0] to the field’s gradient. The field gradient may be fairly small near the surface of a big magnet.
Plenty of things are magnetic dipoles or can be induced to become dipoles in the presence of a magnetic field. Ever played with iron filings and a magnet? Or a ferrofluid and a magnet?
I'm not even sure they reversed the magnet polarity in this video, it seems they just removed the magnet and put it back, so there's no way to rule out a ferromagnetic effect. Again, I just find it really hard to deduce anything from this footage, not saying it can't be a superconductor.
I'm not even sure they reversed the magnet polarity in this video, it seems they just removed the magnet and put it back, so there's no way to rule out a ferromagnetic effect.
I'm not sure either if LK-99 is a type-II superconductor but I would believe so given the papers I've read. Type-II superconductors aren't perfect diamagnets, they allow magnetic flux to penetrate the superconductor once you hit the first critical field, these flux vortices then get pinned at sites of defects where the energy requirement for breaking the superconductivity is lowest. That's what keeps a type-II superconductor levitating over a magnet, a type I superconductor or perfect diamagnet wouldn't do that. Then again I have never seen how e.g. a tiny YBCO flake (high Tc type-II superconductor) would behave if you put it in a beaker and dragged a Neodym magnet below it, so who knows.
I'm a bit skeptical how they even know it's the right material, getting the doping right seemed quite intricate so it would seem quite extraordinary that they can hit the right process after trying for a few days. Not saying they didn't, but so far I'm rather inclined to believe they just got a ferromagnetic metal flake (which is easy to get following the thermal annealing process they did, or even by banging the material up a bit as they seem to have done for getting it out of the synthesis tubes).