3 ms·

Electrons interact with each other. Photons don't, unless you get to extremely high energies. We'll see, I suppose.

splittingTimes 9y ago
> Electrons interact with each other. In principle correct, but in the particular case of Cooper pairs (responsible for the super conduction) the el-el interaction plays a subordinate role. Actually, the Coulomb force is counter-productive to building electron pairs, as electrons repel each other. The effectively attractive el-el coupling of Cooper pairs is mediated by the electron-phonon interaction (Phonons are the quantized lattice vibrations). The following picture might help: When a negatively charged electron moves through the lattice, the positive cores of the lattice ions are attracted and move away from their equilibrium position. This causes a lattice polarization. In metals, the ion movement is much, much slower then that of the electrons. So when the polarization-inducing electron has already moved on, the lattice is still out of its equilibrium position. A second electron that comes into that region, "sees" the lattice polarization and the elongated positive ions and is attracted to it. Thus the lattice vibration has mediated an effectively attractive coupling between the two electrons.
- AnimalMuppet 9y ago
  And, to more directly address filigree's point: The claim is that photons can (indirectly) interact via the same mechanism, because both photons can interact with the atoms they are passing through.
marcosdumay 9y ago
Yeah, electrons repel each other, except when they don't. Superconductors work on that area where they don't really. Condensed matter is a complex subject, full of 2nd, 3rt and higher order effects, and causal loops. And also, a subject where everything is nearly impossible to calculate. Do not expect things to work like you expect there.
- scentoni 9y ago
  Exactly. For instance, electrons in semiconductors have an effective mass that is a tensor, not a scalar. Holes (a missing electron, the semiconductor analog of a positron) typically have effective masses different from electrons.

> Electrons interact with each other. In principle correct, but in the particular case of Cooper pairs (responsible for the super conduction) the el-el interaction plays a subordinate role. Actually, the Coulomb force is counter-productive to building electron pairs, as electrons repel each other. The effectively attractive el-el coupling of Cooper pairs is mediated by the electron-phonon interaction (Phonons are the quantized lattice vibrations). The following picture might help: When a negatively charged electron moves through the lattice, the positive cores of the lattice ions are attracted and move away from their equilibrium position. This causes a lattice polarization. In metals, the ion movement is much, much slower then that of the electrons. So when the polarization-inducing electron has already moved on, the lattice is still out of its equilibrium position. A second electron that comes into that region, "sees" the lattice polarization and the elongated positive ions and is attracted to it. Thus the lattice vibration has mediated an effectively attractive coupling between the two electrons.

AnimalMuppet 9y ago
And, to more directly address filigree's point: The claim is that photons can (indirectly) interact via the same mechanism, because both photons can interact with the atoms they are passing through.

marcosdumay 9y ago

Yeah, electrons repel each other, except when they don't. Superconductors work on that area where they don't really. Condensed matter is a complex subject, full of 2nd, 3rt and higher order effects, and causal loops. And also, a subject where everything is nearly impossible to calculate. Do not expect things to work like you expect there.

scentoni 9y ago
Exactly. For instance, electrons in semiconductors have an effective mass that is a tensor, not a scalar. Holes (a missing electron, the semiconductor analog of a positron) typically have effective masses different from electrons.