STATISTICAL ENSEMBLES AND SPECTRAL CORRELATIONS IN MESOSCOPIC SYSTEMS

Employing different statistical ensembles may lead to qualitatively di fferent results concerning averages of physical observables on the mes oscopic scale. Here we discuss differences between the canonical and t he grandcanonical ensembles due to both quenched disorder and thermody namical effects. We show how these differences are related to spectral correlations of the system at hand, and evaluate the conditions (temp erature, system's size) when the thermodynamic limit is achieved. We d emonstrate our approach by evaluating the heat capacity, persistent cu rrents and the occupation probability of single electron states, emplo ying a systematic diagrammatic approach. (C) 1997 Elsevier Science Ltd .