Circulating currents in a metallic ring with two quantum dots

Abstract

We analyze a system constituted by two single level quantum dots embedded in a metallic ring connected to external electrodes. The energy levels of the dots are controlled by an external gate potential. Additionally, the external electrodes are under the effect of an external applied potential. In these conditions, a circulating current appears in the ring. We show that this current appears when the gate potential is such that the electron-hole symmetry is broken. The direction of circulation depends upon the sign of the external potential and which dot has greater energy. The maximum value of this current is very sensitive to the gate and applied potentials, but it remains finite as the connection between the leads and the ring goes to zero. Therefore, although the circulating current is directly related to the applied potential, it demands a negligible current from the leads. The current is shown to be independent of the ring length, as opposed to the case of a persistent current induced by a magnetic field. It is not a nanoscopic phenomenon, and, as a consequence, it can be orders of magnitude larger than a typical persistent current in a metallic ring.