Electronic Theory for the Transition from Fermi-Liquid to Non-Fermi-Liquid Behavior in High-T_(c) Superconductors

We analyze the breakdown of Fermi-liquid behavior within the 2D Hubbard model as function of doping using our recently developed numerical method for the self consistent summation of bubble and ladder diagrams. For larger doping concentrations the system behaves like a conventional Fermi-liquid and for intermediate doping similar to a marginal Fermi-liquid. However, for smaller doping pronounced deviations from both pictures occur which are due to the increasing importance of the short range antiferromagnetic spin fluctuations. This is closely related to the experimental observed shadow states in the normal state of high-$T_c$ superconductors. Furthermore, we discuss the implications of our results for transport experiments.