Quantization and Stability of Currents in Superconductors

In an electron gas with pairing correlations there exists the possibility of excited states corresponding to a modified pairing of the electrons and associated with "supercurrents." The quantization of these states, which is also reflected in the quantization of flux through a multiply connected superconductor, implies the occurrence of macroscopic "isomerism" providing an immediate explanation of the persistent currents. It is suggested that similar phenomena, associated with vortex lines in the electron fluid, may occur in simply connected samples under suitable conditions.