Persistent currents and role of ‘whispering gallery modes’

Abstract

There have been several studies on persistent currents in mesoscopic systems. Measurements performed on single metal rings have shown that the amount of persistent current is one or two orders larger than what is predicted by various theoretical models. In this paper we examine the role of evanescent wave modes (‘whispering gallery modes’) of transport of coherent electrons around the ring in the phenomenon of persistent currents. We use the analogy from optics where it is established experimentally that these modes have low dissipation and exceptionally large Q values. We expect that existence of such high Q modes for electron transport can result in enhanced persistent currents. These modes may have some role in the current transport in superconducting rings and discs as well, especially when the size of the superconducting ring or disc is small enough. We suggest tunnelling experiments to probe the role of such modes.