We report an optical investigation on the $ab$ plane charge dynamics for ${\text{Na}}_{1-\delta }\text{FeAs}$ single crystal. Formation of a partial energy gap is clearly observed in the magnetic ordered phase. Comparing with the optical response of other FeAs-based parent compounds with high magnetic transition temperatures, both the gap value $2\Delta$ and the energy scale for the gap-induced spectral weight redistribution are smaller in ${\text{Na}}_{1-\delta }\text{FeAs}$. The experimental results favor an itinerant origin of the antiferromagnetic transition.

• Received 2 July 2009

DOI:https://doi.org/10.1103/PhysRevB.80.100507