Topological and transport properties of Dirac fermions in an antiferromagnetic metallic phase of iron-based superconductors.

We investigate Dirac fermions in the antiferromagnetic metallic state of iron-based superconductors. Deriving an effective Hamiltonian for Dirac fermions, we reveal that there exist two Dirac cones carrying the same chirality, contrary to graphene, compensated by a Fermi surface with a quadratic energy dispersion as a consequence of a nontrivial topological property inherent in the band structure. We also find that the presence of the Dirac fermions gives the difference of sign-change temperatures between the Hall coefficient and the thermopower. This is consistent with available experimental data.