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(Fe1-xCox)(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.