Effect of impurities on the current magnification in mesoscopic open rings

We have considered an open system consisting of a metallic ring coupled to two electron reservoirs. We have recently shown that in the presence of a transport current, circulating currents can flow in such a ring even in the absence of magnetic field. This is related to the current magnification effect in the ring. In our present work we have studied the effect of impurity on the current magnification. We find that the presence of impurity can enhance the current magnification in the loop significantly and thus lead to large circulating currents in a certain range of Fermi energies. This is in contrast to the known fact that impurities can only decrease the persistent currents in closed ring in the presence of magnetic flux.