3 ms·

Is this related to how some materials become superconductors at low temperature? Does the slowing down of this electron flux improve the material's ability to c

by sfn42 2y ago

Is this related to how some materials become superconductors at low temperature? Does the slowing down of this electron flux improve the material's ability to conduct electricity or is there some other mechanism at play?

khold_stare 2y ago
Superconductivity is fascinating. I don't know how people were able to come up with the explanations. Crudely, the reduced temperature means less jiggling of the metal lattice. This in turn makes it possible for the nuclei to be pushed around by electrons to form essentially sound waves (phonons) in the lattice (think of the lattice compressing and expanding due to interplay with electrons). At a certain temperature and therefore a certain frequency of lattice oscillation, electrons pair up to form "Cooper pairs" - they move in concert due to the lattice movement. What's crazy is that cooper pairs become a sort of pseudoparticle, and their quantum behaviour is different to regular electrons. Cooper pairs have integer spin (as opposed to half-integer spin), so they no longer obey the Pauli exclusion principle and all the electrons in the entire material basically form one giant condensate that extends through the whole material and can all occupy the same lowest energy quantum state.
- jaybrendansmith 2y ago
  That is the BEST explanation of superconductivity I have ever heard.
  - khold_stare 2y ago
    Thanks for the kind words! For anyone curious to dive deeper into the crazyness that is quantum mechanics I can highly recommend a few resources: - Sean M Carroll's work, in particular his Biggest Ideas in the Universe books: https://www.preposterousuniverse.com/biggestideas/ https://www.preposterousuniverse.com/biggestideas/ - Artur Ekert, basically the father of Quantum Cryptography has an amazing course for free on youtube: https://www.youtube.com/@ArturEkert https://www.youtube.com/@ArturEkert . It's a very precise and understandable explanation of quantum computing, and some of the math that is involved with quantum mechanics. - If you have hours to spare, watch Richard Behiel's videos on Youtube. He's like the 3Blue1Brown of Quantum Physics. His latest video on superconductivity and the Higgs Field is almost 5 hours long (!!!) https://youtu.be/DkH1citHtgs?si=-yQNYDu9TlTpE1A0 https://youtu.be/DkH1citHtgs?si=-yQNYDu9TlTpE1A0 . It builds on his other videos, so I'd recommend starting at the beginning.
- mncharity 2y ago
  > all the electrons in the entire material basically form one giant condensate Very not my field, but perhaps that's "all the paired electrons"? Brief ai-ing (do we have a verb yet?) suggests only some small fraction of conduction electrons form pairs, let alone all the rest.
  - genewitch 2y ago
    "Slop pass"?
  - itishappy 2y ago
    Only Cooper pairs can condensate, but in a superconducting material at the critical temperature Cooper pairs account for nearly all free electrons.
- cyberax 2y ago
  Another way to put it: Cooper pairs become _bound_ objects. And so their energy levels are quantized, and to excite them, you need to apply more energy than is available from the thermal motion of atoms in a superconductor. This doesn't happen with unpaired free electrons because their energy spectrum is pretty close to continuous.
- bigger_cheese 2y ago
  My background is material's science so there might be another meaning physicists use that I'm not familiar with but my very simplified understanding/explanation of Phonons are that they are vibrations within a crystal lattice. These vibrations exists at all temperatures above absolute zero, so I don't think it is accurate to say phonons form due to reduced temperature.
- the-mitr 2y ago
  Similar to superconductors, there are superinsulators, which have an infinite resistance so that no electric current passes through. The phenomenon of superinsulation can be regarded as an exact dual to superconductivity. https://en.wikipedia.org/wiki/Superinsulator https://en.wikipedia.org/wiki/Superinsulator
movpasd 2y ago
Electrons are actually delocalised in a metal: rather than point particles bouncing around the nuclei like a pinball, they're more like waves that ripple and diffract around them. This means that to good approximation, the electrons pass right through each other. Because of this, I don't expect the electron motion to affect resistance much. What definitely affects resistance is the vibration of the nuclei lattice, in which thermal energy is also stored. This vibration makes the electrons more likely to scatter. This means even in a non-superconducting metal, resistivity drops as you get colder. The special thing about superconductors is that there's a temperature where the resistivity suddenly drops to zero. (If you look up "superconductivity resistance against temperature", you'll see some graphs showing what I mean.) I don't know exactly the details of why this happens, but it has something to do with Cooper pairs. Electrons in these states are also sensitive to being knocked out and bumped up to regular conducting states by thermal noise.

by sfn42 2y ago

khold_stare 2y ago

Superconductivity is fascinating. I don't know how people were able to come up with the explanations. Crudely, the reduced temperature means less jiggling of the metal lattice. This in turn makes it possible for the nuclei to be pushed around by electrons to form essentially sound waves (phonons) in the lattice (think of the lattice compressing and expanding due to interplay with electrons). At a certain temperature and therefore a certain frequency of lattice oscillation, electrons pair up to form "Cooper pairs" - they move in concert due to the lattice movement. What's crazy is that cooper pairs become a sort of pseudoparticle, and their quantum behaviour is different to regular electrons. Cooper pairs have integer spin (as opposed to half-integer spin), so they no longer obey the Pauli exclusion principle and all the electrons in the entire material basically form one giant condensate that extends through the whole material and can all occupy the same lowest energy quantum state.

jaybrendansmith 2y ago
That is the BEST explanation of superconductivity I have ever heard.
- khold_stare 2y ago
  Thanks for the kind words! For anyone curious to dive deeper into the crazyness that is quantum mechanics I can highly recommend a few resources: - Sean M Carroll's work, in particular his Biggest Ideas in the Universe books: https://www.preposterousuniverse.com/biggestideas/ https://www.preposterousuniverse.com/biggestideas/ - Artur Ekert, basically the father of Quantum Cryptography has an amazing course for free on youtube: https://www.youtube.com/@ArturEkert https://www.youtube.com/@ArturEkert . It's a very precise and understandable explanation of quantum computing, and some of the math that is involved with quantum mechanics. - If you have hours to spare, watch Richard Behiel's videos on Youtube. He's like the 3Blue1Brown of Quantum Physics. His latest video on superconductivity and the Higgs Field is almost 5 hours long (!!!) https://youtu.be/DkH1citHtgs?si=-yQNYDu9TlTpE1A0 https://youtu.be/DkH1citHtgs?si=-yQNYDu9TlTpE1A0 . It builds on his other videos, so I'd recommend starting at the beginning.
mncharity 2y ago
> all the electrons in the entire material basically form one giant condensate Very not my field, but perhaps that's "all the paired electrons"? Brief ai-ing (do we have a verb yet?) suggests only some small fraction of conduction electrons form pairs, let alone all the rest.
- genewitch 2y ago
  "Slop pass"?
- itishappy 2y ago
  Only Cooper pairs can condensate, but in a superconducting material at the critical temperature Cooper pairs account for nearly all free electrons.
cyberax 2y ago
Another way to put it: Cooper pairs become _bound_ objects. And so their energy levels are quantized, and to excite them, you need to apply more energy than is available from the thermal motion of atoms in a superconductor. This doesn't happen with unpaired free electrons because their energy spectrum is pretty close to continuous.
bigger_cheese 2y ago
My background is material's science so there might be another meaning physicists use that I'm not familiar with but my very simplified understanding/explanation of Phonons are that they are vibrations within a crystal lattice. These vibrations exists at all temperatures above absolute zero, so I don't think it is accurate to say phonons form due to reduced temperature.
the-mitr 2y ago
Similar to superconductors, there are superinsulators, which have an infinite resistance so that no electric current passes through. The phenomenon of superinsulation can be regarded as an exact dual to superconductivity. https://en.wikipedia.org/wiki/Superinsulator https://en.wikipedia.org/wiki/Superinsulator

movpasd 2y ago

Electrons are actually delocalised in a metal: rather than point particles bouncing around the nuclei like a pinball, they're more like waves that ripple and diffract around them. This means that to good approximation, the electrons pass right through each other. Because of this, I don't expect the electron motion to affect resistance much. What definitely affects resistance is the vibration of the nuclei lattice, in which thermal energy is also stored. This vibration makes the electrons more likely to scatter. This means even in a non-superconducting metal, resistivity drops as you get colder. The special thing about superconductors is that there's a temperature where the resistivity suddenly drops to zero. (If you look up "superconductivity resistance against temperature", you'll see some graphs showing what I mean.) I don't know exactly the details of why this happens, but it has something to do with Cooper pairs. Electrons in these states are also sensitive to being knocked out and bumped up to regular conducting states by thermal noise.