Obtaining the electronic structure of the newly discovered iron-based superconductors is the key to understanding the mechanism of their high-temperature superconductivity. We used angle-resolved photoemission spectroscopy (ARPES) to make direct measurements of the electronic structure and Fermi surface (FS) of the untwinned uniaxial state of CaFe2As2, the parent compound of iron-based superconductors. We observed unequal dispersions and FS geometries along the orthogonal Fe-Fe bond directions. More importantly, unidirectional straight and flat FS segments are observed near the zone center, which indicates the existence of a unidirectional nematic charge density wave order, strengthening the case for a quantum electronic liquid crystalline "nematic" phase. Further, the doping dependence extrapolates to a possible quantum critical point of the disappearance of this order in the heavily overdoped regime of these materials.
@article{arxiv.1009.0271,
title = {Uniaxial "nematic-like" electronic structure and Fermi surface of untwinned CaFe2As2},
author = {Qiang Wang and Zhe Sun and Eli Rotenberg and Filip Ronning and Eric D. Bauer and Hsin Lin and Robert S. Markiewicz and Matti Lindroos and Bernardo Barbiellini and Arun Bansil and Daniel S. Dessau},
journal= {arXiv preprint arXiv:1009.0271},
year = {2010}
}