We have investigated the evolution of the electronic properties of the t-t'-U Hubbard model with hole doping and temperature. Due to the shape of the Fermi surface, scattering from short wavelength spin fluctuations leads to strongly anisotropic quasi-particle scattering rates at low temperatures near halffilling. As a consequence, significant variations with momenta near the Fermi surface emerge for the spectral functions and the corresponding ARPES signals. At low doping the inverse lifetime of quasiparticles on the Fermi surface is of order kBT varying linearly in temperature from energies of order t down to a very low energy scale set by the spin fluctuation frequency while at intermediate doping a sub-linear T -dependence is observed. This behavior is possibly relevant for the interpretation of photoemission spectra in cuprate superconductors at different hole doping levels.

We present the results of a self-consistent weak-coupling calculation for the renormalized singleparticle properties in an itinerant antiferromagnet.Multiple spin-wave excitations accompany the carrier motion and lead to incoherent contributions to the electronic spectrum. We evaluate the quasiparticle spectral weight and energy dispersion. In agreement with strong-coupling theories we find the minimum of the dispersion of the quasihole energy to have momentum (+vr/2, +sr/2) and the dispersion to be Hat around the corners of the Brillouin zone. Very good agreement is achieved with available exact diagonalization data.

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Excited states of the nuclei 127Xe and