Fermi-liquid, non-Fermi-liquid, and Mott phases in iron pnictides and cuprates

The role of Coulomb correlations in the iron pnictide LaFeAsO is studied by generalizing exact diagonalization dynamical mean-field theory to five orbitals. For rotationally invariant Hund's rule coupling a transition from a paramagnetic Fermi-liquid phase to a non-Fermi-liquid metallic phase exhibiting frozen moments is found at moderate Coulomb energies. For Ising-like exchange, this transition occurs at a considerably lower critical Coulomb energy. The correlation-induced scattering rate as a function of doping relative to half filling, i.e., δ=n/5-1, where $n=6$ for the undoped material, is shown to be qualitatively similar to the one in the two-dimensional single-band Hubbard model which is commonly used to study strong correlations in high-Tc cuprates. In this scenario, the parent Mott insulator of LaFeAsO is the half-filled $n=5$ limit, while the undoped $n=6$ material corresponds to the critical doping region δc≈0.2 in the cuprates, on the verge between the Fermi-liquid phase of the overdoped region and the non-Fermi-liquid pseudogap phase in the underdoped region.