A long while ago, I brought up the topic of persistent currents in normal metal rings. Please click the link to get the context. The point is, even in a normal metal (as opposed to a superconductor), if you consider a metal ring small enough that the electrons remain quantum mechanically coherent in going about the ring, the electronic wavefunction must remain single-valued. That means that the quantum mechanical phase accumulated by an electron diffusing around the ring back to its starting point (to speak in a semiclassical way) has to add up to an integer multiple of 2 pi. Since magnetic flux through the ring tweaks the accumulated phase (via the Aharonov-Bohm effect), a persistent current develops in the ring to make sure that the total phase (that from the electron motion and that from the resulting Aharonov-Bohm contribution) add up to a multiple of 2 pi. As I'd discussed before, these currents and the magnetic fields they produce tend to be quite small and difficult to detect.
Thursday, April 19, 2012
Persistent currents and an impressive experiment
Posted by Douglas Natelson at 3:51 PM