There are two challenging things here that makes this a discovery. One, making the material, which is extremely difficult to verify as altermagnetic due to the nature of measuring these materials. Two, the measurement, which combines two techniques to distinguish this as separate from antiferromagnetism.

It is a huge push forwards for the budding field since it provides a really nice way to go to a large-scale synchrotron with your altermagnet and study it in detail.

The application is this: We would like to use ferromagnets and spin currents to make spin-electronic devices ("spintronic") where only the spin information is transferred without any large electrical currents. The goal of this is to save energy from Joule heating as spin can flow with significantly lower energy dissipation.

Ferromagnets run into a lot of problems: they have a stray field, so patterned elements will interact and interfere with each other that sets a limit on how dense each nanostructure can be. Antiferromagnets have a big problem: they are extraordinarily difficult to measure and that is a challenge to overcome.

So the benefit that altermagnetic materials presents is a clear union that tries to overcome the problems of both while retaining the strengths of both.

The exact definition of the ordering of an altermagnet is a bit subtle and it mostly comes from an understanding of how the electronic band structure is different as compared with normal antiferromagnets.

Pirate bay and sci-hub get affected by copyright law more than anything else and, to the best of my knowledge, kiwifarms is protected by section 230 in that respect and has always complied with legitimate takedown requests.

What is complicating the interpretation here is the log scale (and lack of conversion to resistivity): It is amplifying the impression of the noise below what they call Tc, and making it harder to interpret the approach of the material to the transition point. The behaviour at the approach to Tc also doesn't really look like a metal, which should scale as propto T, or a semiconductor which should increase with decreasing temperature. Possibly a result of it being some horrible mixed phase ceramic.

Frankly there are too many details missing to trust them. They've fabricated a thin film but not characterized it. It is well known that the properties of a material change when you go from bulk to thin film with a big dependence on the thickness. They don't mention how the resistance of this thin film is measured - that's important for what artifacts you might expect to see in your measurements (van der Pauw vs Hall bar measurements are the standard but they don't mention using either). Without characterizing the thin film it's also difficult to know, chemically and structurally, what you are measuring. I don't see any data confirming the quality of the thin film. The way the data is presented is such that it can be misleading, showing I-V curves instead of resistance when you are really trying to say the resistance is what is changing. The first paper doesn't even mention the insulator-metal transition that is present in the second paper which is bizarre - this is important if you are also claiming a superconductor transition close by and you would expect some discussion of this behaviour.

All of these are things that, one would hope, will be picked up by the reviewers as low hanging fruit before even really delving into the detail of the theory they present.

Decades of experience alone should not be trusted. Anyone can make a mistake, and not all the authors can be present for every experiment.

[1] - https://www.nature.com/articles/d41586-023-02401-2

Especially when they admit to having phase impurities, and it's not really clear how they've gone from bulk sample to measurement sample (are they really measuring just the superconductor or the impurity phase?). Needs addressing, especially when the Cu2S phase impurity seems to have a phase transition of it's own at or around 370K (suspiciously close to where some of their Tc measurements are).

In realistic terms it seems they're grabbing for the prestige without the foundation of crossing their ts. Bad science like this shouldn't be encouraged. It's likely there's not very many groups growing the same material system so they have the time to spare. A paper like this wouldn't be on the arxiv at all if they were 100% sure because they would go straight for the nature publication and take the time to do more follow-up papers while they can.

Edit: to be clear as well, a lot of people are underestimating the time it takes to reproduce a growth even with a manuscript telling you how to do it. People always leave out steps and oversimplify. There is a lot of extra characterization that takes time to double check you have the right material that lines up with what they have here. Only the direct competitors actually already growing this material can do it in a few days.