Observation of an isosceles triangular electronic structure around the excess iron atoms in Fe 1 + δ Te

We present scanning tunneling microscopy and spectroscopy studies around an individual excess Fe atom, working as a local perturbation, in the parent material of the iron-chalcogenide superconductor Fe${}_{1+\ensuremath{\delta}}$Te. Spectroscopic imaging reveals an isosceles triangular electronic structure around the excess Fe atoms. Its spatial symmetry reflects the underlying bicollinear antiferromagnetic spin state and the structural monoclinic symmetry. These findings provide important clues to understanding the role of the excess Fe atoms, which complicate the understanding of the phenomena occurring in iron-chalcogenide materials.