Optical study of the spin-density-wave properties of single-crystalline Na1-δFeAs

We report an optical investigation on the ab plane charge dynamics for Na1-delta 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 Na1-delta FeAs. The experimental results favor an itinerant origin of the antiferromagnetic transition.