Universal persistent currents in mesoscopic metal rings due to long-range Coulomb interactions

We calculate the average persistent current in a mesoscopic metal ring threaded by a magnetic flux in the diffusive regime. It is shown that the classical electromagnetic energy leads to a universal average current of the order of αec/${\mathit{C}}_0$, where α is the fine structure constant, -e is the charge of the electron, c is the velocity of light, and ${\mathit{C}}_0$ is the classical capacitance of the ring. Striking similarities between persistent currents and universal conductance fluctuations are discovered. We suggest a simple experiment to test our theory.