KRAMERS DEGENERACY AND QUANTUM JUMPS IN THE PERSISTENT CURRENT OF DISORDERED METAL RINGS

The ground state of any time-reversal-invariant system of an odd number of electrons moving in a disordered normal-metal ring is doubly degenerate by Kramers' theorem. We argue that the degenerate ground state is current carrying if the electrons experience scattering by a spin-orbit field. The insertion of an Aharonov-Bohm flux phi lifts the degeneracy, thereby causing the zero-temperature persistent current to vary discontinuously with phi at phi = 0. This conclusion holds true irrespective of the presence of electron-electron interactions and potential scattering by impurities.