Abstract
Multiorbital Hubbard model Hamiltonians for the undoped parent compounds of the Fe-pnictide superconductors
are investigated here using mean-field techniques. For a realistic four-orbital model, our results show
the existence of an intermediate Hubbard U coupling regime where the mean-field ground state has a ,0
antiferromagnetic order, as in neutron-scattering experiments, while remaining metallic due to the phenomenon
of band overlaps. The angle-resolved photoemission intensity and Fermi surface of this magnetic and metallic
state are discussed. Other models are also investigated, including a two-orbital model where not only the
mean-field technique can be used but also the exact diagonalization in small clusters and the variational cluster
approximation in the bulk. The combined results of the three techniques point toward the existence of an
intermediate-coupling magnetic and metallic state in the two-orbital model, similar to the intermediatecoupling
mean-field state of the four-orbital model. We conclude that the state discussed here is compatible
with the experimentally known properties of the undoped Fe pnictides.
