Physicists discover a new switch for superconductivity | Hacker News Reader

Physicists discover a new switch for superconductivity

phys.org

149 pointswglb28 comments

Apparently one of the things that happens when a material transitions into a superconducting state is it stretches (by an infinitesimal amount) in the conducting direction. This stretching is not like usual stretching where there’s a change in the actual structure of the material. Rather, it is the bonds between each atom that stretch - pulling them into a slightly different state, one that happens to let electrons flow completely freely (ie superconducting). This “infinitesimal stretching” is usually caused by magnetic alignment, which is induced by super cold temperatures.

But there are a few odd materials, like iron selenide, that don’t seem to show any kind of magnetic alignment despite being able to become superconducting. That’s where the absolute geniuses behind this paper come in. They took a thread of iron selenide and stuck it to a strip of titanium, then physically stretched the titanium. This induced that “infinitesimal stretching” in the iron selenide sample. By examining the sample with X-rays while artificially inducing the stretch, they could detect the mechanism that would usually be the cause of the stretch. Essentially it is sort of like manually spinning the wheels on a car and watching the engine cycle, in order to understand how vehicles work.

Very clever stuff, and it seems like a real advance in understanding superconductivity. The article doesn’t really go into it, but this does suggest there might be a third axis (“super precise tension”), alongside the usual two of “super low temperature” and “super high pressure”, that we can search along to find new superconductors.

That's neat! Is there an arXiv link to the paper? It looks like the Nature link requires a subscription.

I can access it through my university, but there's currently no way to upload papers to sci-hub, and I can't figure out the anonymous login for libgen.rs

If you add any email to your profile, I'll check back within 24 hours and email the copy to you.

I’d love a copy too, this sounds like their methodology will be a very interesting read… not knowing how they tensioned it and precisely what their measurements showed in terms of the superconducting effects, specifically the drop in resistance, is probably going to steal a few brain cycles today to wondering about it and the paper would be a nice way to put my imagination to rest on the topic.

>Apparently one of the things that happens when a material transitions into a superconducting state is it stretches (by an infinitesimal amount) in the conducting direction. This stretching is not like usual stretching where there’s a change in the actual structure of the material. Rather, it is the bonds between each atom that stretch - pulling them into a slightly different state, one that happens to let electrons flow completely freely (ie superconducting). This “infinitesimal stretching” is usually caused by magnetic alignment, which is induced by super cold temperatures.

That kind of sounds like the tipping point when you stretch a rubber band, where the resistance kind of goes off a cliff and gets a lot easier to pull

I appreciate this perspective. It must be noted that it's truly nothing like stretching a rubber band, but your comment gave me sincere joy anyways.

Reminds me of this bit of dialogue from The Doctor's Wife:

    Rory: What is this place? The scrapyard at the end of the universe?
    11:   Not end of. Outside of.
    Rory: How we can we be outside the universe? The universe is everything.
    11:   Imagine a great big soap bubble with one of those tiny little
          bubbles on the outside.
    Rory: OK.
    11:   Well, it's nothing like that.

Thank you for this summary! Very, very cool research.

But might this physical stretching then also allow room temperature superconductors, if not why not?

Theoretically, I guess it could - iron selenide superconducts when its electrons are all forced the outer ring, and physically stretching the material can cause force electrons to the outer ring. But the precision required to apply enough tension to pull the electrons of every single atom into that state is absurd, and if some aren’t in that state then it won’t superconduct. Not to mention you also have to guarantee somehow that the material won’t do all the other things it normally does when physically stretched, like deform or break.

How about a feedback mechanism based on the current flowing itself? Have some piezo thing stretch the material with feedback from a current sensor going though that material to have it always go for the highest current flow.

GP's remark that "the precision required to apply enough tension to pull the electrons of every single atom into that state is absurd" made me want to ask the same thing, so seconding this question.

I assume feedback control is an obvious enough approach that the researchers already checked and rejected it - but I'm curious as to why specifically it would not work. In my layman non-physicist non-material-scientist imagination, I'm thinking of an aggregation of such self-regulating piezo "cells", or even continuous surface tuned to locally stretch/contract "just right" with the current flowing over it (is such a feat even possible)?

Yeah it may be even more precision than what a feedback mechanism can do?

I suppose there is a limit to how linear piezo response can be. I am not sure the order of magnitude of forces involved here, but they must be very,very,very,very small.

So far as I know there is nothing in physics that would prevent such a thing - I think the issue is whatever tensioning device you use (unsure if piezo is the way to go or something else), each unit would be responsible for a relatively small number of atoms (maybe ~10, maybe ~10^6, hard to even guess) which means these devices are probably going to require atomically-precise manufacturing. And any practical application of superconductor material is going to have 10^23 atoms or more. So now you need 10^17 atomically-precise tensioning devices… it’s much easier to let e.g. magnetic fields do this work.

I think the “tension axis” is more likely to be fruitful in a different way, where we find some structure e.g. a crystalline formation that happens to hold atoms apart with just the right amount of tension. But this is all very speculative - the “tension axis” is just a random thought I had while reading the article!

Crazy thought, why not use something like super cooling or pressure get things aligned and then just prevent them from returning back? In other words prevent it from “de-aligning” or returning to the unaligned state? It seems this would be easier.

> But the precision required to apply enough tension to pull the electrons of every single atom into that state is absurd

Easier with individiually-tensioned monofilaments? Graphene monofilaments are interesting because they're very strong; but other materials can be monofilaments, too; just usually they're useless in that form.

Interesting thought about a third axis but isn't tension essentially negative pressure? Superconductivity requires the atoms to be aligned and as still as possible in order for pathways for the electrons to emerge as far as I understand. Like a miniature version of a particle accelerator just without acceleration apart from the push each electron gets from the one behind it. Seems logical that I can get a material to stay put by either pushing or pulling on it on at least two sides.

Maybe the tension is applied perpendicular to the pressure?

Interesting, but would tension and pressure be the same underlying mechanism? eg. pressure along the z axis causes expansion in x-y axes, so is the pressure result really just tension in disguise?

Definitely at the limits of my understanding here, but I don’t believe so. I believe the very high pressures simply force materials into more compact arrangements of bonds.

The problem with this is that pressure is a scalar quantity. "Pressure along the z axis" does not make sense.

Good point. The device being used is a diamond anvil cell [1], which is a uniaxial device and why I thought they were directly applying pressure along a single axis, but that's not quite how the device works.

[1] https://en.wikipedia.org/wiki/Diamond_anvil_cell

So now might be a good time to bring up the patent application from 2017[1] in which the Navy was involved. Titled "Piezoelectricity-induced High Temperature Superconductor", it was fairly widely viewed as disinfo or fringe science back then. Perhaps it's time to reconsider?

[1] https://patents.google.com/patent/US20190348597A1/en

> But the team found that as they stretched the iron selenide, its electrons began to overwhelmingly prefer one orbital state over the other. This signaled a clear, coordinated shift, along with a new mechanism of nematicity, and superconductivity.

That's fascinating! Electron orbitals are determined by quantum mechanics, and I'm really curious about the quantum-mechanical mechanism at work here to cause large numbers of atoms to have electrons in the same orbital.

Like many here I was wowed by the physics of this article but also wanted to say this is some great science writing. Super clear and to the point.

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