Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1-xCox)2As2

M. P. Allan, T-M. Chuang, F. Massee, Yang Xie, Ni Ni, S. L. Bud'ko, G. S. Boebinger, Q. Wang, D. S. Dessau, P. C. Canfield, M. S. Golden, J. C. Davis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

109 Citations (Scopus)


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).

Original languageEnglish
Pages (from-to)220-224
Number of pages5
JournalNature Physics
Issue number4
Publication statusPublished - Apr 2013




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