Static versus adiabatic response of mesoscopic systems: The role of the statistical ensemble

We extend and generalize the notion of ensemble averaging in the context of the thermodynamics of mesoscopic systems. Two important factors determine the statistical ensemble: (i) Constraints imposed on the system as external fields are varied adiabatically; (ii) the initial preparation of the ensemble. Different procedures correspond to different experimental setups, and may result in different magnitude, sign, and Aharonov-Bohm periodicity of the quantity at hand. Adiabatic dynamical response is related to one of these static averaging procedures.