Unidirectional Electronic Structure in the Parent State of   Iron-Chalcogenide Superconductor Fe$_{1+\delta}$Te
  We use scanning tunnelling microscopy and spectroscopy to explore the electronic structure of Fe$_{1.07}$Te which is the parent compound of the iron-chalcogenide superconductors. A unidirectional electronic structure with a period of $a_{0}$ (where $a_{0}$ is the lattice constant) along the a-axis is observed. The unidirectional pattern is visible within an energy range from approximately -200 to +130 meV. Since the direction of the unidirectional electronic structure coincides with those of the underlying antiferromagnetic and the predicted orbital orders, it is presumable that the observed unidirectional structure is closely tied to these orders and is peculiar to the parent state in iron-based superconductors. 
Tadashi Machida, Kazuho Kogure, Takuya Kato, Hiroshi Nakamura,   Hiroyuki Takeya, Takashi Mochiku, Shuuichi Ooi, Yoshikazu M...
cond-mat.str-el