Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1-xCox)(2)As-2

TitleAnisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1-xCox)(2)As-2
Publication TypeJournal Article
Year of Publication2013
AuthorsAllan MP, Chuang TM, Massee F, Xie Y, Ni N, Bud'ko SL, Boebinger GS, Wang Q, Dessau DS, Canfield PC, Golden MS, Davis JC
Journal TitleNature Physics
Volume9
Pages220-224
Date Published04
Type of ArticleArticle
ISBN Number1745-2473
Accession NumberWOS:000316997100013
Keywordsdetwinned ba(fe1-xcox)(2)as-2, iron arsenide superconductor, symmetry, transition
Abstract

Iron-based high-temperature superconductivity develops when the 'parent' antiferromagnetic/orthorhombic phase is suppressed, typically by introduction of dopant atoms(1). But their impact on atomic-scale electronic structure, although in theory rather complex(2-13), is unknown experimentally. What is known is that a strong transport anisotropy(14-25) with its resistivity maximum along the crystal b axis(14-25), develops with increasing concentration of dopant atoms(14,20-25); this 'nematicity' vanishes when the parent phase disappears near the maximum superconducting T-c. The interplay between the electronic structure surrounding each dopant atom, quasiparticle scattering therefrom and the transport nematicity has therefore become a pivotal focus(7,8,12,22,23) of research into these materials. Here, by directly visualizing the atomic-scale electronic structure, we show that substituting Co for Fe atoms in underdoped Ca(Fe1-xCox)(2)As-2 generates a dense population of identical anisotropic impurity states. Each is similar to 8 Fe-Fe unit cells in length, and all are distributed randomly but aligned with the antiferromagnetic a axis. By imaging their surrounding interference patterns, we further demonstrate that these impurity states scatter quasiparticles in a highly anisotropic manner, with the maximum scattering rate concentrated along the b axis. These data provide direct support for the recent proposals(7,8,12,22,23) that it is primarily anisotropic scattering by dopant-induced impurity states that generates the transport nematicity; they also yield simple explanations for the enhancement of the nematicity proportional to the dopant density(14,20-25) and for the occurrence of the highest resistivity along the b axis(14-25).

URL<Go to ISI>://WOS:000316997100013
DOI10.1038/nphys2544