Symmetry breaking via orbital-dependent reconstruction of electronic structure in detwinned NaFeAs

The superconductivity discovered in iron pnictides is intimately related to a nematic ground state, where the C sub(4) rotational symmetry is broken via the structural and magnetic transitions. We here study the nematicity in NaFeAs with polarization-dependent angle-resolved photoemission spectroscopy. A uniaxial pressure was applied on the sample to overcome the twinning effect in the low temperature C sub(2)-symmetric state and obtain a much simpler electronic structure than that of a twinned sample. We found the electronic structure undergoes an orbital-dependent reconstruction in the nematic state, primarily involving the d sub(xy)- and d sub(yz)-domina ted bands. These bands strongly hybridize with each other, inducing a band splitting, while the d sub(xz)-domina ted bands only exhibit an energy shift without any reconstruction. These findings suggest that the spin fluctuations at high temperatures and their coupling with the orbital degree of freedom could be the dominant force to drive the nematicity, while the ferro-orbital ordering between d sub(xz) and d sub(yz) orbitals can only play a minor role here.