One odd thing that I've not seen any discussion on: the reported heat capacity of LK-99 decreases above 250K, which is pretty atypical. Has there been any commentary on that?
German, but nevertheless: http://blog.fefe.de/?ts=9a3f8740
"I work in the field [...] we don't believe a word of this. [...] The data set in Fig. 4(b) is also a treat. It is VERY unusual when the heat capacity decreases again at high temperatures. This can happen at low temperatures, but not at high temperatures. [...] My personal assumption is that the authors measured an insulator, so no current flow and therefore no voltage occurred (4-point measurement). This would look like a superconductor. But if you then turn up the current (i.e. the applied voltage), breakdowns may occur and a current begins to flow. That would explain the sharp increase."
This isn't 1 experiment as the Germans seem to think. There are multiple papers, patents, etc.
The main focus of these papers has been to make huge claims and make replication very easy. They are "all in" and they want others to call.
If they were bluffing they would be heavy on results and light/secretive on how to make the stuff (trade secret, etc).
That's why there are 2x papers published within 3 hours, both with different authors, and you have one author telling New Scientist he did not approve of a paper naming him as an author.
That might be your interpretation of it. I think the Germans would call it being straightforward.
But the papers don’t show that. There’s no obvious contradiction unless you make some big assumptions.
A more plausible idea IMO is that it could be a 4-point measurement of a highly inhomogeneous sample. If the current probes make contact with conductive parts of the sample, and there is a conductive path between them, but one or both voltage probes are not contacting the conductive path, then the voltage measurement would be garbage and potentially zero.
I don’t think this is much of a problem when measuring conventional conductors (you don’t need a particularly good contact, which is much of the point), but a lot of superconductors are oddball materials where, under conditions where they fail to superconduct, they barely conduct at all.
So maybe the sample has a conducting phase and an insulating phase?
I know they were formed from sulfur compounds, but the production process should have eliminated those compounds, and the final forming is done in a vacuum so there shouldn't be any oxide generation to form non-conductive barriers.
I don't know much about the process but shouldn't they be testing resistance in a superconductor?
https://www.oxfordlearnersdictionaries.com/definition/englis...
And we very much are talking about an alloy, which is a "metallic substance composed of two or more elements"
https://www.britannica.com/technology/alloy
Lead is a metal. Copper is a metal, a combination of 2 metals is an alloy.
However, you are right, I did overlook that the compound is an oxide, my bad.
A 4-point measurement of an insulator would show zero current, as far as I know.
"I work in the field and we discussed the preprint a bit in the research group this morning. In a nutshell, we don't believe a word of it:
Fig. 1(a) and (c) are implausible. Normally, this sort of thing looks like this. Note the gradual increase at low currents, this effect is especially expected for magnetic fields.
Also Fig. 1(d) cannot be correct. At Tc ~ 400K the Meissner effect would displace a much stronger field than 10 Oe = 1 mT. I.e. the distinction between FC (field cooled) and ZFC (zero-field cooled) should not be so pronounced. It should look more like this.
But in this case the temperature dependence does not agree at all with the critical currents of Fig. 1(a) and (c).
And also that ALL values in Fig. 1(d) are negative is extremely unusual, but this could perhaps be argued.
The data set in Fig. 4(b) is also a treat. It is VERY unusual to see the heat capacity decrease again at high temperatures. This can happen at low temperatures, but rather not at high temperatures.
I know the described experimental setup / cryostat very well. There is no reasonable reason why the authors did not measure at higher temperatures to show that the behavior above Tc ~ 400K is significantly different. E.g. a temperature dependence of the resistance would have been mandatory.
In general, the paper is very poorly written. The data are not adequately discussed, the explanations are poor, and the papers cited are rather, shall we say, meager. This does not inspire confidence in what the authors have measured and want to have seen there.
My personal guess is that the authors measured an insulator, accordingly no current flowed, and thus no voltage occurred (4-point measurement). Then it looks like a superconductor. But if you then turn up the current (i.e. the applied voltage), there may be breakdowns and a current starts to flow. This would explain the sudden increase."