# Drift velocity of electrons in a superconducting loop

Do electrons travel at the Fermi velocity in a superconducting loop?

For metals the Fermi velocity seems to be around $10^6$ m/s.

So would electrons (in a Cooper pair) travel around the loop at this velocity if no voltage is applied?

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The drift velocity obviously isn't the Fermi velocity otherwise the current would be enormous. I guess you're asking if any particular pair would be moving at a steady Fermi velocity, because there's no scattering to hinder it. I guess so, though for every pair moving at the Fermi velocity in one direction there will be another pair moving at the Fermi velocity in the other direction so the net, i.e. drift, velocity would be zero. – John Rennie Mar 14 '14 at 10:35
Are all Cooper pairs in a superconductor in exactly the same coherent state? I suppose this state has equal components traveling clockwise and counter clockwise around the loop. – John Eastmond Mar 14 '14 at 10:43
@John Eastmond: If there is a semiconductor annulus, but there is no magnetic field in the hole, then I expect the Cooper pair field to have the same complex value everywhere. That means: there is no motion. If there are some quanta of magnetic flux locked in the hole, then the complex argument will make exactly the same number of turns around the annulus. In this case the gradient will exist, but “velocity” is not a well-defined concept for a wavefunction on an annulus. In any case, these “equal components traveling clockwise and counter clockwise” seem like a puzzle to me. – Incnis Mrsi Aug 14 '14 at 17:38