The superconductivity of layered graphene | Hacker News Reader

The superconductivity of layered graphene

newscientist.com

134 pointswesturner33 comments

Physicist here. The superconductivity in layered graphene is indeed surprisingly strange, but this popular article may not do it justice. Here are some older articles on the same topic that may be more informative:

https://www.quantamagazine.org/how-twisted-graphene-became-t...,

https://www.quantamagazine.org/a-new-twist-reveals-supercond....

Let me briefly say why some reasons this topic is so interesting. Electrons in a crystal always have both potential energy (electrical repulsion) and kinetic energy (set by the atomic positions and orbitals). The standard BCS theory of superconductivity only works well when the potential energy is negligible, but the most interesting superconductors --- probably including all high temperature ones like the cuprates --- are in the regime where potential energy is much stronger than kinetic energy. These are often in the class of "unconventional" superconductors where vanilla BCS theory does not apply. The superconductors in layered (and usually twisted) graphene lie in that same regime of large potential/kinetic energy. However, their 2d nature makes many types of measurements (and some types of theories) much easier. These materials might be the best candidate available to study to get a handle on how unconventional superconductivity "really works". (Besides superconductors, these same materials have oodles of other interesting phases of matter, many of which are quite exotic.)

Thank you for the additional info and links. This is why I love HN comments

While we have you, have any new theories or avenues of research come out of the lk99 stuff or was it completely just hype and known physics?

BCS == Bardeen–Cooper–Schrieffer [0].

[0] https://en.wikipedia.org/wiki/BCS_theory

Also physicist here. I've worked on conventional superconductors, but never on unconventional ones. Last I heard, it was believed to be mediated by magnons (rather than phonons). Who claims it is due to Coulomb interaction?

I think everything we don't have a model for is surprisingly strange. Gravity only seems "normal" because we've been teaching a reasonable model for it for hundreds of years - Aristotle thought things fell to the ground because that was "their nature", but thought it quite weird. X-Rays seem bonkers unless you've grown up with them, and there is something deeply unnerving about genetics, quantum and even GenAI until you've spent some time pulling apart the innards and building an explainable model that makes sense to you. And even then it can catch you out. More ways to explain the models help normalise it all - what's now taught at 9th grade used to be advanced post-doc research, in almost every field. And so it goes on.

2D superconductors don't make much sense because, as the article says, theory is behind experimentation here. That's also why there is both incredible excitement, but also a worry that none of this is going to stack up to anything more than a bubble. My old Uni (Manchester) doubled down hard on the work of Geim and Novoselov by building a dedicated "Graphene Institute", after they got the Nobel Prize, but even 15 years after that award most people are still trying to figure out what does it all actually mean really? Not just in terms of the theory of physics, but how useful is this stuff, in real world usage?

It'll settle down in due course. The model will become apparent, we'll be able to explain it through a series of bouncing back between theory and experiment, as ever, and then it won't seem so strange any more.

I'm not sure that'll ever be true of quantum computing for me, but then I am getting a bit older now...

It’s interesting to think what in people’s personal perception makes them find strange thing interesting or scary or boring. Especially when it comes to grapheme.

Imagine doing computing on grapheme clusters.

That's what I thought LLMs did

I still don’t believe explanations for gravity…let alone dark matter!

Not believing an explanation for dark matter seems prudent. It's just the name we've given to a certain set of observations not matching how we believe the universe works. We're still piecing together the details.

Relevant xkcd tooltip: https://xkcd.com/1489

Do you suppose everything is explainable? Gravity feels to me like the sort of thing that just sort of is. I'm all for better characterizations of it, but I'm not holding my breath for an answer to: why?

Everything may be explainable, just not by humanity.

How does our biology affect the limits of what we can comprehend?

Oh plenty of ways probably. I expect there are perspectives out there which would have a look at our biggest questions and find them to be mundane with obvious answers but which would themselves boggle at concepts that we consider elementary.

But here I am in this body, and not that one, so I'm content to accept an axiom or two.

the question is depth and quality of explainability as determined by the predictive power those explanations provide...

Gravity is something very simple. It cannot be a complex thing, because it demonstrates a very simple behavior.

There are plenty of cases where a complex thing has very simple behavior. For centuries, brewers could get away with a mental model for yeast as something that multiplies and converts sugar to alcohol until it can't anymore. It took quite a jump in technology to realize just how fantastically complex the inner workings of a yeast cell is.

I'm not proposing that gravity is underpinned by something complex, just that if its mechanism is out of our reach then so to are any conclusions about that mechanism's complexity.

I also think that gravity is complete bunk. Funny how there's suddenly Graphene everywhere from dental applications to injectibles.Weird times.

> My old Uni (Manchester) doubled down hard on the work of Geim and Novoselov by building a dedicated "Graphene Institute", after they got the Nobel Prize, but even 15 years after that award most people are still trying to figure out what does it all actually mean really? Not just in terms of the theory of physics, but how useful is this stuff, in real world usage?

That's the beauty of real research. There's no guarantees it'll pan out. But it's generally worth doing and spending (sometimes decades of) time exploring. Too many people have become infatuated with instant gratification. It's pervasive even in young, scientific minds. The real gratification is failing that same test 100 times until you finally land on a variation that might work. And then figuring out why it worked.

Edit: And if that success never comes, the gratification is graduating and moving on to more solvable problems, but bringing with you the scientific methods you learned along the way. Scientists might spend their whole lives working on something that won't work and that's okay. If that isn't for you, go into product dev.

When I was a kid, magnets seemed magical. I'm 60 now, and they still seem like magic, despite always having some on hand to play with.

Magnets, how do they work? It's surprisingly complicated actually!

Miracles!

My interest with these overlapping lattices is the creation of fractional electric charges (Hall effect) and through, essentially, Moiré patterns. The angle of alignment will make a big effect.

Let me make an artifact to demonstrate… brb

It reminded me of a DOOM glitch that you get with a zero-width wall.

I'm curious what glitch you mean, maybe you can find a link describing it? All of my googling just turns up arbitrary problems that often end up being due to poorly authored maps. :)

https://doomwiki.org/wiki/Moir%C3%A9_error

https://claude.site/artifacts/f024844e-73c2-4eb1-afc9-401f3d...

Here you go. See how there are different densities and geometries at different angles. These lattice overlays can create fractional electrical charges — which is very strange — but how this affects super conductivity is unclear.

Very cool example!

Slightly different preprint variants:

https://arxiv.org/abs/2406.13742

https://arxiv.org/abs/2406.13740v2

This is exciting, sounds like new theory incoming (or possible way to test existing string/other theories?). I'd love to see PBS Spacetime or some other credible outlet explain the details of the experiment / implications for mere mortals.

Is this exactly 1.1 degrees?

Or is it 1.09955742876?

What I mean -- did they round up, is there some connection to universal constants?

Edit: I don't understand where the 1.1 degrees comes from. Why is it 1.1 and not something else...

It's not exactly a single ultra-specific 1.1000000... degree value only, just values approximately close to that. As to what the connection is: that's what the research is trying to unearth more about.

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