The two-fluid description of a mesoscopic cylinder

Quantum coherence of electrons interacting via the magnetostatic coupling and confined to a mesoscopic cylinder is discussed. The electromagnetic response of a system is studied. It is shown that the electromagnetic kernel has finite low frequency limit what implies infinite conductivity. It means that part of the electrons is in a coherent state and the system can be in general described by a two-fluid model. The coherent behavior is determined by the interplay between finite size effects and the correlations coming from the magnetostatic interactions (the interaction is considered in the mean field approximation). The related persistent currents depend on the geometry of the Fermi surface. If the Fermi surface has some flat portions the self-sustaining currents can be obtained. The relation of the quantum coherent state in mesoscopic cylinders to other coherent phenomena is discussed. Received: 9 July 1997 / Revised: 19 September 1997 / Accepted: 4 November 1997