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The temperature and frequency dependences of the conductivity are derivedfrom optical reflection and transmission measurements of electron dopedBaFe$_2$As$_2$ crystals and films. The data is consistent with gap nodes orpossibly a very small gap in the crossover region between these twopossibilities. This can arise when one of the several pockets known to exist inthese systems has extended s-wave gap symmetry with an anisotropic piececanceling or nearly so the isotropic part in some momentum direction.Alternatively, a node can be lifted by impurity scattering which reducesanisotropy. We find that the smaller gap on the hole pocket at the $\Gamma$point in the Brillouin zone is isotropic s-wave while the electron pocket atthe $M$ point has a larger gap which is anisotropic and falls in the crossoverregion.

Nodes in the Order Parameter of Superconducting Iron Pnictides Observed by Infrared Spectroscopy