Noninteger flux quanta for a spherical superconductor

A thin-film superconductor shaped into a spherical shell at whose center lies the end of long thin solenoid in which there is an integer flux NΦ₀ has been previously extensively studied numerically as a model of a two-dimensional superconductor. The emergent flux from the solenoid produces a radial B field at the superconducting shell and N vortices in the superconducting film. We study here the effects of including a second solenoid (carrying a flux f) which is inserted inside the first solenoid but passing right across the sphere. This Aharonov-Bohm (AB) flux does not have to be quantized to make the order parameter single valued. The Ginzburg-Landau free energy is minimized at fixed N as a function of f and it is found that the minimum is usually achieved when the AB flux f is half a flux quantum, but depending on N the minimum may be at f=0 or values which are not obvious rational fractions.