
Evidence for superconductivity above 260 K at megabar pressures (2018) - based2
https://arxiv.org/abs/1808.07695
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tasty_freeze
I've seen this research cited a few times (perhaps even here on HN) and every
time the conversation is centered on whether this is practical or the
naysayers moaning how this isn't practical.

The research isn't intended for commercial, practical use. There is no point
in discussing it in such terms.

The interesting thing is that this behavior was predicted by models, and the
experiment confirms the model. That is it. Perhaps with increased confidence
in the models it will lead to improvements in practical superconductors in
time, but not now.

~~~
Roritharr
As you seem to understand this topic a bit more: can you explain the model?

What is the current theory how superconductors work?

~~~
pdonis
_> What is the current theory how superconductors work?_

The best general model of superconductivity I'm aware of is still the BCS
model:

[https://en.wikipedia.org/wiki/BCS_theory](https://en.wikipedia.org/wiki/BCS_theory)

This model basically says a superconductor is a Bose-Einstein condensate,
where the Bose "particles" are pairs of electrons in the material that are
entangled via an interaction involving low-energy vibration states of the
material as a whole. The problem is that this general model doesn't tell us
what the critical temperature for the Bose-Einstein condensation is. We have
to find that out by a combination of experimentation with different materials,
and more detailed extensions of the model that test various hypotheses about
what kinds of material properties should affect the critical temperature. This
paper is just a recent development in that line of research.

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pitaj
The necessary pressure isn't that important. Obviously using this material
under those conditions in the real world won't be realistic.

However, what this shows is that superconductivity is possible at those
temperatures, and that pressure is a factor to further investigate when
experimenting with other candidate materials.

~~~
JumpCrisscross
> _pressure is a factor to further investigate when experimenting with other
> candidate materials_

There are crystals which retain their internal strain after release. This is
valuable research.

~~~
anfilt
Isnt growing crystal under high pressure in presses also not well understood?
Like how are you going to make long traces or intricate structure in a high
pressure environment that dont fully know growth and forming process of such
crystals?

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londons_explore
This occurs at 2 million bar (pressure).

From an engineering perspective, what does it take to contain such pressures,
and would it be possible to make 'wire' consisting of a pressure-maintaining
jacket surrounding the conductor?

Anyone want to do the maths? How much Kevlar are we talking...?

~~~
semi-extrinsic
What you need is a material with very high ultimate tensile strength. Carbon
nanotubes _might_ do it. Let's check.

To compute the burst pressure of a pipe, we can use Barlow's formula:

P_max = S * T /R

where T is wall thickness, R is radius of the outside of the pipe, and S is
ultimate tensile strength. Here T=R is the limit where the inside radius is
zero. So the best case is

P_max = S/1.0000001

Carbon nanotubes are the highest strength material, with a theoretical S=100
megabar. So not possible, sadly.

~~~
bArray
This is far outside my wheel house, but... Surely it's the pressure
differential that dictates the burst pressure? So if you had multiple sleeves,
each decreasing in pressure as you get closer to the outside, this could be
possible?

~~~
saagarjha
I'd expect that for a pipe under high pressure but small pressure differential
compressive strength would matter much more than tensile strength.

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jnurmine
Stupid question from a non-physicist: what exactly does the high pressure do
here? How does it contribute to the superconductivity?

~~~
Tomminn
I'm guessing it essentially increases the elastic constants of the material;
that is, increases the "spring constants" of the bonds between atoms. As a
result, the resonant frequency of acoustic vibrations rises. When these
acoustic vibrations are quantized into phonons, the minimum energy of each
phonon therefore rises, since it is proportional to this resonant frequency.
Since conventional cooper pairs are pairs of electrons bound by a phonon, this
increases the binding energy of the pair, and makes it more resilient to being
broken up by the thermal energy.

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chicob
Putting P-T into context, the conditions involved in synthesizing some forms
of lanthanum decahydride are enough to create diamonds.[1]

The cubic phase of LaH10 is synthesized around 170 GPa and 1000 K.[2] The SC
properties arise ~10 centigrade below the freezing point of water, but still
under enormous pressure (190 GPa).

So if a sample of graphite were cooked aside during the synthesis of cubic
LaH10, it would have become a diamond by the end of the experiment.

[1]
[https://en.wikipedia.org/wiki/Diamond#Thermodynamics](https://en.wikipedia.org/wiki/Diamond#Thermodynamics)

[2] [https://sci-hub.se/10.1002%2Fanie.201709970](https://sci-
hub.se/10.1002%2Fanie.201709970) (This paper shares some authors with the
paper to which this post links.)

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phoe-krk
That's over one million atmospheres of pressure we are talking about here. Are
there any predictions of how this is going to affect modern-day electronics
that will be unable to undergo such massive pressure?

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lachlan-sneff
Perhaps it would be possible to contain materials at such high pressures
inside other materials like carbon nanotubes or diamonoid structures?

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goda90
Maybe we can get to some happy medium where it's a practical level of pressure
and cooling, not quite room temperature but still something we can use.

~~~
nine_k
Liquid nitrogen is almost that already. It's readily available, reasonably
cheap, and you just need Styrofoam for the bulk of the insulation.

The superconducting material itself is expensive, brittle, hard to fabricate,
and hard to work with.

~~~
heisenzombie
Standard "high-temperature" superconducting wire (e.g. YBCO) isn't actually
all that bad to handle or wind. You buy it extruded in a metal matrix (usually
copper), and treat it only a little bit more gently than standard copper wire.

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markhahn
let's all move to megabar!

