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Comment by p-e-w | Hacker News Reader

> One cannot measure superconductivity with an ordinary ohmmeter.

But one can measure electrical resistivity, and if the material's resistivity is much lower than that of ordinary materials, that would be super interesting and valuable, regardless of whether it is a "true" superconductor or not.

If this relatively cheap material had a resistivity around 1/100th that of copper, that would be an engineering breakthrough, and determining that doesn't seem to require a super complicated lab setup.

Do we have an upper bound on LK-99's resistivity, and is that upper bound substantially lower than the resistivity of typical conductors?

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I think you are missing the point: a typical ohmmeter would have metal probes, so with a superconductor you would just be measuring the resistance of those probes. Any attempt to overcome that problem probably introduces a lot of chances for error or noise, or require some huge sample of the superconductor.

Zero resistance would be hard to proof this way, but why can't you compare measurements of LK99 with known conductors?

You absolutely can, and as you can see in this paper it is absolutely do-able to measure the resistance of these materials. They measure an insulator with something on the order of 10^6 ohm m. For reference, copper has a resistivity of ~ 10^(-8) ohm m, so there are about 14 orders of magnitude of difference. This does make the contact resistance pretty negligible in this case too.

I have the same thoughts. I think it's because they are not EEs and want to play with the material. A sensing resistor is trivial.

https://www.digikey.com/en/articles/fundamentals-of-current-...

if you were talking about a meter long segment of pure LK99 you'd have a point. But the pieces in question are so small that even if the LK99 were just copper their resistance would be so low that experimental error in a casual test would be substantial compared to the resistance.

Measuring the resistance would also be frustrated by the superconductive material being scattered in the mass separated by highly resistive impurities, making it easy to get a false negative.

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