Confusion over the formation of cooper pairs Hi all, There are 2 points I do not get: 1. I read something saying that phonon is an energy packet of "heat and sound", and propagates through lattice vibration...so, I thought it is saying that phonon is emitted by one electron, then absorbed by the lattice (and excited one of its vibration mode), then (the phonon) re-emitted via vibration, finally absorbed by another electron. But when I read on, I found that the electron-phonon interaction is a direct process between 2 electrons (one emitted a phonon, another one immediately absorbed it, nothing to do with lattice). So what is the role of "lattice vibration" playing in this phonon exchanging process? Or what exactly is "phonon exchange between electrons"? 2. How can it possible that "a cooper pair travel in one direction, but 2 electrons have opposite momenta (means travelling in opposite direction)"? Just desperately asking...how can this happened? Thanks so much for helping!!