Superconductor question

[itex]\theta[/itex] is the phase of the order parameter [itex] \psi = |\psi|e^{i \theta} [/itex]. Since [itex]\psi[/itex] must be single valued at some specific angular position [itex]\phi + 2k \pi[/itex] on the ring, we need, [itex]\psi(\phi ) = \psi(\phi + 2m \pi ) [/itex], or we need [itex]e^{i \theta ( \phi )} = e^{i \theta ( \phi + 2m \pi)}[/itex], for all m. For the phase factor to remain unchanged over integral number of traversals of the loop, the phase [itex]\theta[/itex] must itself change by only an integer multiple of [itex]2 \pi [/itex] (since [itex]e^{2in \pi} = 1 [/itex]).

So
[tex]\theta ( \phi + 2m \pi ) = \theta ( \phi) + 2n \pi [/tex].

In other words
[tex]\hbar\oint\nabla\theta dl = \hbar \Delta\theta = \hbar (\theta ( \phi + 2 \pi ) - \theta ( \phi)) = 2 \pi n \hbar = nh[/tex]

 

Good answer, Gokul.

In your opinion, from an experimental point of view, what would be a simple method to effect a change in the phase of the wavefunction of the supercurrent while remaining below T(c)?

Creator

 

Have a magnetic flux through the loop. That, after all, is how a SQUID works.

Zz.

 

True, in theory; but by what method are you going to change the length of a brittle superconducting wire while it is in the superconducting state?

 

Of course; externally applying B thru the loop. I should be more specific. I guess I am referring to a non-electromagnetic method of altering the quantum phase.

Creator