Speci c Heat Anomaly and Adiabatic Hysteresis in DisorderedElectron Systems in a Magnetic

We consider the thermodynamic behavior of a disordered interacting electron system in two dimensions. We show that the corrections to the thermodynamic potential in the weakly localized regime give rise to a non monotonic behavior of the speciic heat both in temperature and magnetic eld. From this eeect we predict the appearance of adiabatic hysteresis in the magnetoconductance. Our results can be interpreted as precursor eeect of formation of local moments in disordered electron systems. We also comment on the relevance of our analysis in three dimensional systems. The recent discovery of a B = 0 metal-insulator transition (MIT) in high mobility silicon MOSFETs 1] has revived the interest in disordered electron systems. Whereas conventional scaling theory predicts no metallic state in two dimensions 2] the experiments show a metallic temperature dependent resistivity with a characteristic exponential behavior. Although there have been attempts to interpret these experimental ndings within a phenomenological single parameter scaling theoryy3], there is growing experimental evidence as witnessed by magnetic eld measurements 4] that electron-electron interaction in the spin channel is relevant and needs explicit consideration. Based on the existing theory of disorder and interactionn5], it has been pointed out recentlyy6] that the very existence of a metallic state at low temperatures is indeed possible because of enhanced spin uctuations, though a more thorough understanding of the behavior of various physical quantities is doubtless required. In particular it has been suggested that magnetoconductance in parallel eld and tun-neling measurements should provide good diagnostic tests for this theory.