Electronic nematic phase, which breaks C₄ rotational symmetry, has been reported widely in iron-based superconductors [1].  The electronic nematic phase is suggested to be related to Cooper pair formation of unconventional superconductivity in iron-based superconductors [2].

In this study, we observed the electronic nematic domains in the hole-doped iron-based superconductor Ba_1-xNa_xFe₂As₂, with x = 0.18, by using laser photoemission electron microscopy (laser-PEEM). Laser-PEEM has both a high spatial resolution (92 nm) and a wide field of view(5 ~ 40 μm) suitable to observe electronic nematic domains. In the previous work, laser-PEEM measurements have been conducted in FeSe and BaFe₂(As, P)₂ which are both non-doped materials [3]. In the present study, we focused on the effect of hole-doping on electronic nematic domains.

The electronic nematic domains in Ba_1-xNa_xFe₂As₂ were clearly observed below the structural transition temperature Ts ~ 114 K. We also analyzed the domain wall thickness ξ_nem, which is proportional to the correlation length of the electronic nematic phase, by using Ginzburg-Landau theory. We found that the domain wall thickness ξ_nem is smaller than the spatial resolution (92 nm), whereas FeSe and BaFe₂(As, P)₂ have large ξ_nem, 550 and 450 nm, respectively [3]. This difference can be explained by the modification of the Fermi surface due to the hole doping. This result indicates that the correlation length of the electronic nematic phase is sensitive to the hole doping, providing important information to understand the electronic nematic phase.

[1] R. M. Fernandes et al., Nat. Phys. 10, 97 (2014).
[2] K. Mukasa et al., Nat. Commun. 12, 381 (2021)
[3] T. Shimojima et al., Science 373, 6559 (2021).

Keywords: Iron-based superconductor, Electronic nematic phase