SPECTRAL CORRELATIONS IN DISORDERED MESOSCOPIC METALS AND THEIR RELEVANCE FOR PERSISTENT CURRENTS

We use the Lanczos method to calculate the variance sigma(2)(E, phi) o f the number of energy levels in an energy window of width E below the Fermi energy for noninteracting disordered electrons on a thin three- dimensional ring threaded by an Aharonov-Bohm flux phi. We confirm num erically that for small E the flux-dependent part of sigma(2)(E, phi) is well described by the Altshuler-Shklovskii-diagram involving two Co operons. However, in the absence of electron-electron interactions thi s result cannot be extrapolated to energies E where the energy-depende nce of the average density of states becomes significant. We discuss c onsequences for persistent currents and argue that for the calculation of the difference between the canonical- and grand canonical current it is crucial to take the electron-electron interaction into account.