Magnetic susceptibility of disordered nondiffusive mesoscopic systems

Disorder-induced spectral correlations of mesoscopic quantum systems in the nondiffusive regime, and their effect on the magnetic susceptibility, are studied. We perform impurity averaging for nontranslational invariant syste ms by combining a diagrammatic perturbative approach with semiclassical tec hniques. This allows us to study the entire range from clean to diffusive s ystems. As an application we consider the magnetic response of noninteracti ng electrons in microstructures in the presence of weak disorder. We show t hat in the ballistic case (an elastic mean free path I larger than the syst em size) there exist two distinct regimes of behavior depending on the rela tive magnitudes of I and an inelastic scattering length L-phi. We present n umerical results for square billiards, and derive approximate analytical re sults for generic chaotic geometries. The magnetic-field dependence and the Ln dependence of the disorder-induced susceptibility are qualitatively sim ilar in both types of geometry. [S0163-1829(99)02020-2].