Can you tell us more about why it is an interesting property?
> The -233°C threshold (40 K), often associated with the McMillan limit, marks a boundary beyond which conventional superconductivity theories become less predictive.
So it’s like finding a gas giant exoplanet that’s in the “wrong” place. We understand Jupiter and Saturn. We don’t understand a gas giant orbiting its star in ten days. Thats weird. And science can’t progress when there is nothing “weird”. It means all the data matches our models. It’s boring. It has nothing to teach.
A ten day orbit or a normal metal group superconductor are outside our comfort zone and may mean new physics.
We have two classes now, copper and iron based superconductors that work at room temperature above 40K or so. Below 40K, there are countless superconductors and the mechanism they use breaks down at around 40K. There's no reason to think that a material which is a superconductor below 40K will have some variant that is one above 40K.
Once we have evidence of superconductivity above 40K or so (at normal pressures) things change. Those materials follow different rules that we only partially understand. And there is reason to hope that variants exist which will be superconductors at even higher temperatures. There's no set barrier or upper limit once you cross the 40K threshold. One may exist, but we don't know it.
What happened with copper, and iron (to a much lesser extent), is that we marched up the curve and eventually made superconductors with many real-world. Once you reach 77K (-195C) we're in business. The hope is that maybe we can do the same with nickel. This has traditionally only really worked well with copper-based compounds.
Having a 3rd class of materials gives us a lot more options. And the more examples we have, the more likely we are to come up with some useful theory.
https://arxiv.org/abs/2406.08129
The McMillan limit has been challenged before