I'm trying to imagine how these extreme pressures would modify bond angles, nuclei spacing, and constraints on motion. And also tring to understand how that's affecting the behavior and creation of the Cooper pairs.
First concept, virtual particles vs real particles. When we talk about "an electron flowing through metal" it is not actually a single electron. As it moves, the electron will move into an atom, another gets knocked out. But in aggregate it "acts like" a single particle with possibly different properties from a real electron. For example it likely has a different mass. A virtual photon will travel slower than a real one. And so on.
Virtual particles can even correspond to things that aren't particles at all! For example sound is a wave, and quantum mechanically is carried by virtual particles known as phonons. These act exactly like any other particle, even though they are actually aggregate behavior of lots of other things!
A Cooper pair is a pair of things (eg electrons) that are interacting enough that they have a lower energy together than they would apart. Electrons are fermions, with half spin. They have a variety of properties, such as the Fermi exclusion principle. A bound pair of electrons becomes a virtual particle with an integer spin. Which makes it a boson, which behaves differently.
Superconductivity happens when charge is carried by bosons.
In high temperature superconductors, it looks like the electrons are at least partially bound by interaction with phonons. The high pressures change the speed of sound, and therefore change how easily Cooper pairs form.
However https://phys.org/news/2019-04-mechanism-high-temperature-sup... claims that there is now a theoretical explanation for high temperature superconductors, and the best guess above doesn't seem to be the real explanation. The real explanation being that the feature/TIQ-7651_unique_schema_version
Remember what I said about particles having a different mass moving through materials? The binding together of electrons through interaction with phonons seems to depend on the mass of the electrons. When you squeeze the lattice, that mass decreases.
This is the Pauli exclusion principle, in case someone wants to learn more on the subject.
Interesting. Do we know if it possible to disrupt superconductivity with sound at just the right frequency? And the converse, has anyone tried to enhance superconductivity by using sound (i.e. increase either the critical temperature, increase the current density, etc)?
Besides this new example with superconductivity, there are other more familiar phase transitions with the same behavior.
For example, with most liquids, in order to solidify them you may either cool them or compress them.
The same if you want to liquefy gases, either cooling or compressing has the same effect.
Room-temperature superconductivity at very high pressures has been predicted many years ago, but it is very nice to have an experimental confirmation.
The other knob you can use to change the vibrations is the mass of the balls. This can be done by using different isotopes of the same element and the critical temperature goes down with mass.
I don't quite remember my intro to electrical components, though it's a quick read for the basics. The GP obviously knows about atom models and band gap.
The paradox bit is that, as far as I can tell pressure is roughly equivalent to heat, and heat equals decreased intrinsic conductivity. But if I imagine that high preasure restricts the absolute motion of particles, that would equal decreased resistance (like an idealized fixed suspension for your swing, that doesn't take energy out of the system).
Since Hydrogen is involved, I suppose there's a channel of Hydrogen rumps without any electrons, and the high preassure is needed to keep the hydrogen from moving apart and recombining outside the ensemble. Surely this involves some form of entanglement? Which I imagine as a kind of clockwork, all cores spinning in unison.
Haha, I have no idea what I'm talking about.
The equal charges participate on the problem, but do not stop the electrons from pairing up. There is a lot of virtual particle exchange between them, but that's how forces happen. It's more correct to say that the crystal mechanically constrains the electrons into pairs than that the electrons pair with virtual particles.
(IANAP, but this one topic I have studies a little.)
Now a superconductor is just a conduit for electrons that doesn't generate heat. We know from Landauer's principle that heat is only generated when you destroy information. If I take a pair of entangled electrons, those electrons contain exactly one bit of information (in the von neumann sense). If I cannot add energy in excess of the energy required to disentangle them, then that bit of information is never destroyed.
Whether or not a given interaction between the electron pair and the substrate has enough energy to disentangle them is not a function of temperature, it is a function of the actual energy that may be imparted to my pair. Which is proportional to the actual heat in my material, rather than its temperature.