A magnetic levitation demo indicates a possible Meissner effect (which is refuted here by this paper), and this is so much easier than a resistance measurement, which is a delicate task and susceptible to experimental errors. So levitation is used as a quick "first check", especially when you don't have a full lab setup to do other tests, which are much more complicated (in addition to a levitation test or a resistance measurement, one can also measure its frequency-dependent magnetic susceptibility curve, temperature-dependent specific heat curve, or its Josephson effect).

One cannot measure superconductivity with an ordinary ohmmeter. Electrodes, wires and the ohmmeter itself are resistive, the meter can never show zero ohms. You need to set an experiment up with a current source and a voltmeter to measure the IV curve across the material [1]. Even then, the voltmeter will never show "zero" volt because of noise, which needs to be minimized in the experiment and removed during post-processing. In this case, sample preparation is also problematic as the synthesized material is not uniform. And your measurement is also expected to be temperature-dependent to show the material's transition to a superconductor. It's more involved than seeing it floating on a magnet, to say the least.

[1] It's basically the same 4-wire Kelvin sensing used by all milli-ohmmeters. But to characterize superconductivity, you need to do even better. https://en.wikipedia.org/wiki/Four-terminal_sensing

Do you have any idea on what the ballpark cost is to do these replication experiments I keep reading about? Or the more complicated experiments you mention?

Asking out of curiosity as I would have assumed it's very expensive but there seem to be many groups of varying sizes doing these and quite quickly which I would have thought would be extremely wasteful but may suggest it's more economically feasible than I had thought.

> 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?

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.

This question has been asked with near identical or very similar wording in almost every LK-99 submission I've seen over the last week or so... Is there something botnet-y happening? I find it hard to believe anyone reading similar threads could have missed the numerous answers to this and similarly-formed questions that have been offered lately.

It could be the sheer volume of discussion. I've seen a lot of these posts and this is the first time I've read this question.

Maybe it's because I have been obsessively ensuring that I read every comment on every top thread... Some kind of selection bias could be at play...

The top comment on every thread about every new thing on HackerNews is a half-assed debunking of it

I’ve been half assedly following this, not understanding a single word in the papers that keep coming out, not understanding the musings of enthusiasts and professionals

and it looks like I know just as much that its a nothing burger, with maybe some sliver of novelty

we dont have a superconductor, as expected

Exactly. Almost every thread has this query. And surprisingly its always on the top.

At least nobody has asked about the real-world technology implications in this thread yet.

now I have to get out my bingo card and ctrl+f "hoverboard" and "maybe purity",

It’s a natural question when reading about this, like asking why a police officer makes a suspected drunk driver walk a line instead of measuring BAC.

Not everyone reads every (or any!) paper and story.

Yes, and it is getting a little annoying at this point to be frank.

Not all of us read HN every day or follow each discussion. A lot of people don’t read the comments at all.

Maybe it is the most natural question which comes to a lay person like me when it comes to superconducting. Not everyone can be as knowledgeable, or in the loop as you are.

And I assure you that I am no bot. I acquire sustenance, go into low energy states and have a lifetime warranty like all fellow meatbags.

That is exactly what a bot would say... you have to prove you are human by starting a company and making $1M

Wait, you got a lifetime warranty? xD

Yep. It gets void when I die

Generated samples are too small and powder-like to test for that without a lot of difficulties.

Note: I'm not a physicist. Just my understanding from reading.

The samples are super small and not homogeneous, so its tough to get any kind of accurate reading with probes, is my understanding.

Because the production of lk-99 yields a puddle of mess.

https://twitter.com/MarkTyler81/status/1688736978437898240

LK-99 == alchemy RT SC.