I think the more likely explanation is that the particles do touch each other but the interface is not superconductive. In other words, it is a polycrystalline material, and most of it is LK-99, but the grain boundaries are not a very good conductor. In conventional superconductors grain boundaries don't disrupt superconductivity because they are 3D superconductors, but in this allegedly 1D superconductor the superconducting channels in most cases don't meet at the grain boundaries, so the current has to overcome the resistance of some material that is almost an insulator.
If that is the case it will be difficult to produce a material that is macroscopically superconducting. But I hope researchers will be able to make single crystals that are large enough for resistance measurements so that finally it can be determined if this material is a superconductor or not. For practical uses the best result that can be achieved with this material may be a metal-LK-99 composite where the LK-99 particles lower the resistivity of the metal by 50-90%.
The Korean team appears to have been stuck for several years by the lack of reproducibility of this synthesis method. While it was a great discovery that has shown that this material must have some very interesting properties, perhaps even superconductivity at ambient temperature and pressure, in order to be able to measure its properties and be able to evaluate the possible practical applications, a much more precise method for enforcing the desired crystal structure is required, than mixing powders and baking them into a ceramic.
Perhaps such a method for producing samples with deterministic properties would be to develop first a method to grow monocrystals of the special kind of lead phosphate that forms the base crystal structure, maybe by drawing the crystals from melt.
Once monocrystals of this kind of lead phosphate are available, they could be doped with copper, e.g. by ion implantation. By controlling and varying the parameters of the process, e.g. the angle of incidence and the velocity of the ions and the thermal profile used for annealing, it is likely that reproducible samples can be produced, where the copper ions substitute lead in the useful places and not in the others.
By this method it would be possible to produce only thin layers of LK-99, but that should be enough to enable the characterization of the material.
Moreover, because LK-99 is very fragile, it is unlikely that it could be used to make cables or coils. Practical uses where LK-99 would be deposited as thin films are much more likely.
As an alternative to ion implantation, which might be able to produce thicker layers, perhaps once monocrystals of the base lead phosphate are available it may be possible to develop some method of chemical vapor deposition, to grow epitaxially a layer of LK-99 over the base crystal, but with such a method it is less obvious if there is any way to control which lead atoms are substituted, though this may depend on the orientation of the base crystal.
Looking at the Griffin paper, the Pb(2) site is described as being 1.08eV 'more energetically favorable'. I am having trouble understanding what this means.
Years back I did MOCVD semiconductor fabrication research, I never reached a mastery of it but I am still trying to leverage that understanding here.
During growth, adatoms that incorporate into proper crystal lattice locations enter a lower energy state compared to those in imperfect locations. The energy state is lower in the sense that it requires more energy to remove them from that location. Hence careful control of temperature allows you to selectively favor incorporation into these low energy locations e.g. choose a temperature high enough to remove adatoms from 'imperfect' locations but low enough to not remove them from 'perfect' (low energy) locations.
So when the author says 'energetically favorable' am I to understand this means the Pb(2) location represents a lower energy state (i.e. more difficult to remove Cu from this location) or the opposite? Or something else entirely?
https://arxiv.org/abs/2308.01723
>In fact, I find that Cu on this Pb(2) is 1.08 eV more energetically favorable than Cu on the Pb(1) site, suggesting possible difficulties in robustly obtaining Cu substituted on the Pb(1) site.
https://arxiv.org/abs/2307.16892
The paper from Dr. Griffin at LBNL suggests copper atoms have to be placed in a specific (but less likely) position in the molecule to result in the desired flat band characteristic. Also, the original authors and the labs who were able to replicate LK-99 are reporting they had to make multiple batches to even find a tiny piece that shows levitation. This suggests that you just have to be very lucky to produce a sample with high enough concentration of LK-99 to observe levitation.
If we can somehow confirm that LK-99 is truly a room temperature superconductor, billions of dollars of R&D fund will pour in to improve the fabrication process. When the first transistor was invented, people probably weren't imagining that we'll be mass producing them in nanometer scale in the future. Or maybe LK-99 will be stuck in a lab like graphene. Who knows?
There is a good classic primer on FT-ICR, mostly focused on analysis (mass spectrometry) but also mentioning activation energies for reactions and measurement of kinetics etc.
https://warwick.ac.uk/fac/sci/chemistry/research/oconnor/oco...
If you dunk a bunch of chemicals (for simplicity think wet chemistry) in a vial, all reactions and side reactions are simultaneously occuring, so one has little control over what happens on an atomic scale.
FT-ICR can be used to observe the state AND to manipulate the state. Its like having a compact particle collider, but instead of the high (TeV) energy in CERN etc. its just chemical energy levels.
It happens in high vacuum, so low densities of species, hence not amenable to mass production.
But the instrument is both eyes and hands: one can identify the frequencies corresponding to each ionized molecule, and selectively energize or de-energize specific species to encourage or prevent main and competing reactions, by pumping or damping specific frequencies.
One may build up a molecule in elementary steps and eject finished molecules. Those steps can occur at the same time in the same vessel. Its like having a miniature digitally controlled chemical plant, without having to redo all the pipework if you decide to use a different pathway here or there.
https://sci-hub.ru/https://link.springer.com/article/10.1007...
The difference now is that we're seeing a premature preprint being replicated in real time.
Even in that paper, the authors note: "The way the samples have been prepared seems to be of crucial importance: Michel et al. [21] obtained a single-phase perovskite by mixing the oxides of La and Cu and BaCOa in an appropriate ratio and subsequent annealing at 1,000 ~ in air. We also applied this annealing condition to one of our samples, obtained by the decomposition of the corresponding oxalates, and found no superconductivity." And you can see that in their resistivity/temperature graph of samples prepared using different protocols.
Considering how that preprint has sparked interest in other research institutions and multiplied the resources allocated to the problem, I would say this publication was not premature, it's most other research results that are late.
Ah, so you're saying that superconductivity is not actual zero resistance, but something close to it, and in fact only a factor of 1000x less resistive than the best conductor?
If that is so, this is something that I had previously thought would make a lot more sense to me.
But in that case it's not intuitive to me how SMES is possible with a 0% discharge rate. Shouldn't a significant fraction of the electrons looping around the coils be lost after many loops? (I know very little about electricity, as you can probably tell, never mind superconductors).
For high temperature superconductors (50-70+K), it's not literal zero for superconducting mechanisms discovered so far.
A bigger issue is going to be sample size. A 1mm-diameter 1mm-long rod of silver has a resistance of about 20 μΩ (or 2e-5) at room temperature. That's already getting tricky to measure with lab-grade equipment without pushing insane currents through it, let alone anything even smaller. If you want to measure a 1m-diameter 1m-long silver rod (which would be 0.02μΩ or 2e-8) you could just push a few thousand amps through it and reliably measure that using a household multimeter in the mV range - but do that with a small sample and it'll evaporate.
Not that low in range though, you will end up seeing thermal noise that dwarfs your measurement.
Showing diamagnetism is one of the least error-prone ways to demonstrate the superconductor effect.
That’s my understanding anyway.
No, a badly attached probe would usually show a larger resistance, not a smaller one. That's actually the easiest error to make, making improper contact with the sample. The resistance is measured indirectly using a reference current. So you'd measure a higher resistance or a break rather than zero if a probe were not attached correctly (unless the two voltage probes are touching but that would normally speaking be spotted).
The diamagnetism is simply easier to verify using an impure or small sample.
[1] https://www.ni.com/docs/en-US/bundle/ni-daqmx/page/measfunds...
You can mesaure current by electrical fields, but have the same issues as before. Your testing equipment and your very tiny sample sizes.
The way to think of this is simple: you can't measure anything without subtle joining the circuitry that you are measuring and that has an effect on the properties of the circuit as a whole for which you have to compensate. In this case: the voltage measurement is going to consume a tiny bit of power and that is due to the resistance of the measurement apparatus even if it isn't in the main current path but a secondary one. But the people that do these kinds of measurements tend to be well aware of this and will pick their measurement gear and reference current to minimize the chances of that happening.
if the area is small, couldn't it be "badly attached" directly to the other probe?
The first LK-99 paper used this method to claim zero resistivity, but people complained that if the inner probes lost contact, that would also be consistent with their data. This criticism doesn't totally make sense to me, since the apparent superconductivity came and went in the expected way as they changed an external magnetic field. I don't understand how a loose terminal could mimic that figure (I think it was in figure 1).
However, if they perfect 1d production, they can layer in a bunch of them to create a quasi 2d or 3d superconductor.
You can inject a current into a superconducting coil and take measurements of the resultant magnetic field as the current circles for an indefinite period of time. I'm not able to see how this approach analogizes to water in a cup.
And even if not, what you would need is to measure the change of the field over time. This has finite resolution, so you can't distinguish no resistance from very very small resistance.
Yes it could be some tiny resistance, but the same issue occurs with the resolution/accuracy of the voltage or current measurement you would make.