Charge Density Waves in Small Metallic and Superconducting Rings

Experimental results concerning persistent currents in small rings threaded by a magnetic flux do not agree with theoretical predictions, especially for experiments performed in diffusive regime. This suggests important role of disorder in these experiments. In this paper we demonstrate how impurities present in ring modify the persistent current by generating or enhancing charge density waves. The electronic correlations are taken into account for both repulsive as well as attractive electron-electron interaction. The calculations are carried out for one-dimensional rings consisting of up to 12 lattice sites using Lanczös exact diagonalization approach, and for finite-width much larger rings using the Bogolyubov-de Gennes equations.