Translational symmetry breaking in the electronic nematic phase of BaFe2As2

Abstract

The microscopic origin of the nematicity, namely, four-fold rotational symmetry breaking in iron-based superconductors has been controversial since its discovery. In particular, its relationship with the stripe-type spin-density-wave order and the orthorhombic lattice distortion in the antiferromagnetic orthorhombic (AFO) phase, which exists at temperatures below the electronic nematic phase, has been highly debated. Here, we report on the temperature evolution of angle-resolved photoemission spectra of the parent compound BaFe2As2, ranging from the AFO to nematic to paramagnetic phases. The Dirac cone feature, which is formed in the AFO phase, is found to persist in the nematic phase, suggesting that an antiferroic order of the same periodicity as the AFO phase persists in the nematic phase. Considering the relatively shallow d_xy orbital in BaFe2As2, we propose that an antiferro-orbital order involving the d_xy and other orbitals takes place in the nematic phase.