Spectral Evidence for Emergent Order in Ba${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$

Abstract

We report an angle-resolved photoemission spectroscopy study of the iron-based superconductor family, Ba${}_{1-x}$Na${}_x$Fe${}_2$As${}_2$. This system harbors the recently discovered double-Q magnetic order appearing in a reentrant C${}_4$ phase deep within the underdoped regime of the phase diagram that is otherwise dominated by the coupled nematic phase and collinear antiferromagnetic order. From a detailed temperature-dependence study, we identify the electronic response to the nematic phase in an orbital-dependent band shift that strictly follows the rotational symmetry of the lattice and disappears when the system restores C${}_4$ symmetry in the low temperature phase. In addition, we report the observation of a distinct electronic reconstruction that cannot be explained by the known electronic orders in the system.