The Role of Density of States Fluctuations in the Normal State Properties of High Tc Superconductors
HTS show many puzzling anomalies in their normal state properties. Among them are: - the presence of a peak in the c-axis resistance and its growth in external magnetic field - the anomalous negative magnetoresistance observed above Tc - the deviation from the Korringa law in the temperature dependence of the NMR relaxation rate - the opening of a large pseudo-gap in the c-axis optical conductivity well above Tc - the gap-like tunneling anomalies observed above Tc - the anomalies in the thermoelectric power above Tc We show how all these effects can be explained by the enhanced role played in quasi-2D systems by the fluctuation decrease of the one-electron density of states (DOS) at the Fermi level, and its competition with other fluctuation contributions (AL, MT). The full fluctuation theory in HTS is reviewed and its resuls compared with experimental data.