The observation of electronic nematic domains in the iron-based superconductor (Ba, Na) Fe2As2
*Yoichi Kageyama1, Asato Onishi1, Kousuke Ishida1, Cédric Bareille2, Yuta Mizukami1, Toshiyuki Taniuchi2, Kenichiro Hashimoto1, Shigeyuki Ishida3, Hiroshi Eisaki3, Shik Shin4, Takasada Shibauchi1

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 Ba1-xNaxFe2As2, 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 Ba1-xNaxFe2As2 were clearly observed below the structural transition temperature Ts ~ 114 K. We also analyzed the domain wall thickness ξnem, which is proportional to the correlation length of the electronic nematic phase, by using Ginzburg-Landau theory. We found that the domain wall thickness ξnem is smaller than the spatial resolution (92 nm), whereas FeSe and BaFe2(As, P)2 have large ξnem, 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