  We show that previously measured small Fermi surface pockets within the
antiferromagnetic phase of SrFe2As2 and BaFe2As2 are consistent with a Dirac
dispersion modulated by interlayer hopping, giving rise to a Dirac point in
k-space and a cusp in the magnetic field angle-dependent magnetic quantum
oscillation frequencies. These findings support the existence of a nodal
spin-density wave in these materials, which could play an important role in
protecting the metallic state against localization effects. The speed of the
Dirac fermions in SrFe2As2 and BaFe2As2 is found to be 14-20 times slower than
in graphene, suggesting that the pnictides provide a laboratory for exploring
the effects of strongly interacting Dirac fermions.
