Itinerant-Localized Duality Picture of Spin Fluctuations in High-TcCuprates. I. Nested Spin-Fluctuation Theory

The mode-mode coupling theory of spin fluctuations in the normal state of high- T c cuprates is developed on the basis of the itinerant-localized duality picture of technically nested two-dimensional metals. This offers a unified description of the anomalies observed in the normal state of high- T c cuprates. The so-called “spin-gap” behaviors of the resistivity, the specific heat, the uniform spin susceptibility, and the optical conductivity are characterized by the energy scale T * of the crossover between the itinerant and the localized spin fluctuations, while those of the Hall coefficient, the thermo-electric power, the longitudinal NMR relaxation rate, and the neutron scattering intensity, are characterized by different energy scales less than T * . The integrated weight of the nested spin fluctuation decreases when decreasing the temperature or approaching the perfect nesting, leading to the “spin-gap” behavior.