Elementary excitations in the metallicCuO2planes of high-Tcsystems

We determine from a two-band Hubbard Hamiltonian the spin susceptibility and the self-energy for the holes in the ${\mathrm{CuO}}_2$ planes. From this, the quasiparticle lifetime τ, the spectral density, the electrical resistivity ρ resulting from spin scattering, and the NMR relaxation rate 1/${\mathit{T}}_1$ at Cu sites are calculated. Our results, which are expected to be valid for larger hole doping, are in reasonable agreement with experiment and indicate that an interplay of narrow-band phenomena and spin fluctuations leads to the observed anomalous normal-state properties. It is shown how to extend the theory to smaller hole doping when local magnetic moment behavior should be more pronounced.