Electronic reconstruction through the structural and magnetic transitions in detwinned NaFeAs

We use angle-resolved photoemission spectroscopy to study twinned and detwinned iron pnictide compound NaFeAs. Distinct signatures of electronic reconstruction are observed to occur at the structural ( T S ) and magnetic ( T SDW ) transitions. At T S , C 4 rotational symmetry is broken in the form of an anisotropic shift in the orthogonal d xz and d yz bands. The magnitude of this orbital anisotropy rapidly develops to near completion upon approaching T SDW , at which temperature band folding occurs via the antiferromagnetic ordering wave vector. Interestingly, the anisotropic band shift onsetting at T S develops in such a way as to enhance the nesting conditions in the C 2 symmetric state, and hence is intimately correlated with the long-range collinear antiferromagnetic (AFM) order. Furthermore, similar behaviors of the electronic reconstruction in NaFeAs and Ba(Fe 1− x Co x ) 2 As 2 suggest that this rapid development of large orbital anisotropy between T S and T SDW is likely a general feature of the electronic nematic phase in the iron pnictides, and the associated orbital fluctuations may play an important role in determining the ground state properties.