[HN Gopher] Physicists discover a new switch for superconductivity
___________________________________________________________________
Physicists discover a new switch for superconductivity
Author : wglb
Score : 125 points
Date : 2023-06-26 14:02 UTC (8 hours ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| fwlr wrote:
| 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.
| naasking wrote:
| 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?
| eis wrote:
| 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.
| howenterprisey wrote:
| Maybe the tension is applied perpendicular to the pressure?
| distortedsignal wrote:
| That's neat! Is there an arXiv link to the paper? It looks like
| the Nature link requires a subscription.
| reaperman wrote:
| 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.
| hammock wrote:
| >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
| carabiner wrote:
| Physics speculation by SWE's considered harmful. You're
| referring to rubber's elastic limit, at which point it yields
| to plastic (permanent) deformation. This of course has
| nothing to do with electrical conductivity.
| reaperman wrote:
| 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.
| Karellen wrote:
| 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.
| Aardwolf wrote:
| But might this physical stretching then also allow room
| temperature superconductors, if not why not?
| fwlr wrote:
| 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.
| derefr wrote:
| > 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.
| polishdude20 wrote:
| 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.
| TeMPOraL wrote:
| 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)?
| bartchamdo wrote:
| 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.
| reaperman wrote:
| Thank you for this summary! Very, very cool research.
| JoshTriplett wrote:
| > 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.
___________________________________________________________________
(page generated 2023-06-26 23:01 UTC)