Energy-Resolved Real-Space Imaging of Orbital Nematicity in an Fe-Based Superconductor

Electronic nematicity in Fe-based superconductors is manifested by spontaneous rotational symmetry breaking and the formation of nematic domains with mutually orthogonal directions of $d_{xz}$/$d_{yz}$ orbital anisotropy. However, its energy dependence has remained largely unexplored in real space. Using 5.82-eV laser-excited photoemission electron microscopy (laser-PEEM) with an energy-selective slit, we visualize the evolution of linear dichroic (LD) contrast within individual nematic domains of Ba$_{1-x}$Na$_x$Fe$_2$As$_2$ ($x\approx0.08$). We discover a sign reversal of the LD contrast at an energy $\sim0.4$ eV below the Fermi level, directly revealing an inversion of orbital anisotropy inside each domain. This behavior reflects a different energy-dependent redistribution of spectral weight between the $d_{xz}$ and $d_{yz}$ states, highlighting the crucial role of orbital-selective coherence in the nematic phase of Fe-based superconductors.