Current magnification and circulating currents in mesoscopic rings

We show that seveeral novel effects related to persistent currents can arise in open systems, which have no analogue in closed or isolated systems. We have considered a system of a metallic ring coupled to two electron reservoirs. We show that in the presence of a transport current, persistent currents can flow in a ring even in the absence of magnetic field. This is related to the current magnification effect in the ring. In the presence of a magnetic field we show that the amplitude of persistent current is sensitive to the direction of current flow from one reservoir to another. Finally, we briefly discuss the persistent currents arising due to two nonclassical effects namely, Aharonov-Bohm effect and quantum tunneling