Fluctuations of persistent current

TL;DR

This paper provides a theoretical analysis of equilibrium fluctuations of persistent current in nanorings, revealing conditions for their persistence at zero temperature and how their noise spectrum can be tuned by magnetic flux.

Contribution

It introduces a theoretical framework for understanding persistent current fluctuations, including explicit calculations of noise power and the influence of quantum coherence.

Findings

Persistent current fluctuations persist at zero temperature if the current operator does not commute with the Hamiltonian.

The noise power spectrum exhibits sharp peaks at interlevel transition frequencies in a quantum particle model.

In multi-channel rings, the noise spectrum becomes smoother and broader, and can be tuned by magnetic flux.

Abstract

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 smoother and broader PC noise spectrum is expected. A specific feature of PC noise is that its spectrum can be tuned by an external magnetic flux indicating the presence of quantum coherence in the system.