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

Abstract

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${}_2$ ($x\approx 0.08$). We discover a sign reversal of the LD contrast at an energy $\sim 0.4$ 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.

14 pages, 4 figures

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