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alberliu

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- TL;DR Summary
- How do Cooper pairs carry a current with zero net-momentum?

One of the first starting points of introducing BCS theory in a superconductor is applying a theorem stating that the ground-state of a quantum system has an expectation value for its momentum of zero. You then use this to say that an electron must pair with another electron of equal and opposite momentum to form a Cooper pair.

If this is the case, how does this zero-momentum state result in a finite supercurrent? Maybe this is a frame-of-reference issue, but it's not clear to me how you get net charge movement in one direction with a net momentum of zero.

If this is the case, how does this zero-momentum state result in a finite supercurrent? Maybe this is a frame-of-reference issue, but it's not clear to me how you get net charge movement in one direction with a net momentum of zero.