Quantum of London and spin-(l/2)

Summary

According to London, the magnetic flux through a loop of electric charges should be quantized in units ofĦc/q; a result obtained by eliminating the external vector potential by a phase transformation of the wave function of the electric charges. For spin-(l/2) systems, the quantum of London should be divided by 2, as observed. This is shown by including a largescale rotation of the spins: a rotation of 2π about a fixed axis changes the sign of spinors, and this sign is reestablished by a rotation of the phase of the wave function by π, half the quantum of London. This relies upon the basic symmetries of groundstate wave function under phase shift and spin rotation.