Pseudogap formation above the superconducting dome in iron pnictides

Abstract

The nature of the pseudogap (PG) in high transition temperature (high ${T}_{c}$) superconducting cuprates has been a major issue in condensed matter physics. It is still unclear whether the high ${T}_{c}$ superconductivity can be universally associated with the PG formation. Here we provide direct evidence of the existence of the PG phase via angle-resolved photoemission spectroscopy in another family of high ${T}_{c}$ superconductor, iron pnictides. Our results reveal a composition-dependent PG formation in the multiband electronic structure of BaFe${}_{2}$(As${}_{1\ensuremath{-}x}$P${}_{x}$)${}_{2}$. The PG develops well above the magnetostructural transition for low $x$, persists above the nonmagnetic superconducting dome for optimal $x$, and is destroyed for $x$ \ensuremath{\sim} 0.6, thus showing a notable similarity with cuprates. In addition, the PG formation is accompanied by inequivalent energy shifts in the $zx/yz$ orbitals of iron atoms, indicative of a peculiar iron orbital ordering which breaks the fourfold rotational symmetry.