Zero-Point Fluctuations and the Quenching of the Persistent Current in Normal Metal Rings

In a weakly disordered metal electron interactions are responsible for both decoherence of the quasi-particles as well as for quantum corrections to thermodynamic properties. We consider electrons which are interacting with two-level-systems. We show that the two-level-systems enhance the average equilibrium (``persistent'') current in an ensemble of mesoscopic rings. The result supports the recent suggestion that two puzzles in mesoscopic physics may be related: The low temp...

Persistent currents in mesoscopic normal metal rings represent, even a decade after their first experimental observation, a challenge to both, theorists and experimentalists. After giving a brief review of the existing -- experimental and theoretical -- results, we concentrate on the (proposed) relationship of the size of the persistent current to the phase breaking rate. In particular, we consider effects induced by noise, scattering at two-level systems, and magnetic impuri...

An interacting quantum dot inserted in a mesoscopic ring is investigated. A variational ansatz is employed to describe the ground state of the system in the presence of the Aharonov-Bohm flux. It is shown that, for even number of electrons with the energy level spacing smaller than the Kondo temperature, the persistent current has a value similar to that of a perfect ring with the same radius. On the other hand, for a ring with odd number electrons, the persistent current is ...

Recent experiments renewed interest in persistent currents in mesoscopic normal-metal rings. We show that in ballistic rings in high magnetic fields the Zeeman splitting leads to periodic current quenching with period much larger than the period of the persistent current. Simple arguments show that this effect might be relevant for diffusive rings as well. Another aim of this paper is to discuss fluctuations of the persistent current due to thermal excitation of high energy l...

We show that several 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 magnetic field we show that the amp...

We demonstrate that persistent current in meso- and nanorings may fluctuate down to zero temperature provided the current operator does not commute with the total Hamiltonian of the system. For a model of a quantum particle on a ring we explicitly evaluate PC noise power which has a form of sharp peaks which become broadened for multi-channel rings or in the presence of dissipation. PC noise can be tuned by an external magnetic flux which is a fundamental manifestation of qua...

The persistent current, i.e. the equilibrium direct electric current circulating in realistic rings, some authors interpreted as dissipationless in spite of non-zero resistance of the rings, whereas the other one suppose that this current can not decay at dissipation. The observation of potential difference connected with the persistent current may give new important information about paradoxical nature of this quantum phenomena observed in nanostructures.

We study the persistent current circulating along a mesoscopic ring with a dot side-coupled to it when threaded by a magnetic field. A cluster including the dot and its vicinity is diagonalized and embedded into the rest of the system. The result is numerically exact. We show that a ring of any size can be in the Kondo regime, although for small sizes it depends upon the magnetic flux. In the Kondo regime, the current can be a smooth or a strongly dependent function of the ga...

The authors have measured the magnetic response of 33 individual cold mesoscopic gold rings, one ring at a time. The response of some sufficiently small rings has a component that is periodic in the flux through the ring and is attributed to a persistent current. Its period is close to h/e, and its sign and amplitude vary between rings. The amplitude distribution agrees well with predictions for the typical h/e current in diffusive rings. The temperature dependence of the amp...

We theoretically analyze equilibrium fluctuations of persistent current (PC) in nanorings. We demonstrate that these fluctuations persist down to zero temperature provided the current operator does not commute with the total Hamiltonian of the system. For a model of a quantum particle on a ring we explicitly evaluate PC noise power which has the form of sharp peaks at frequencies set by the corresponding interlevel distances. In rings with many conducting channels a much smoo...