Unexpected Fermi-surface nesting in the pnictide parent compounds BaFe₂As₂ and CaFe₂As₂ revealed by angle-resolved photoemission spectroscopy

We use angle-resolved photoemission spectroscopy to study the band structure of BaFe₂As₂ and CaFe₂As₂, two of the parent compounds of the iron arsenic high-temperature superconductors. Our high quality data reveals that although the Fermi surface is strongly three-dimensional, it does indeed have long parallel segments along the k_z direction that can lead to the emergence of magnetic order. More interestingly, we find very unusual incommensurate nesting of the Fermi surface in the a-b plane that is present only at low temperatures. We speculate that this is a signature of a failed charge density wave state that was predicted by renormalization-group studies. ©2010 The American Physical Society