|Title||Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1-xCox)(2)As-2|
|Publication Type||Journal Article|
|Year of Publication||2013|
|Authors||Allan, MP, Chuang, TM, Massee, F, Xie, Y, Ni, N, Bud'ko, SL, Boebinger, GS, Wang, Q, Dessau, DS, Canfield, PC, Golden, MS, Davis, JC|
|Type of Article||Article|
|Keywords||detwinned ba(fe1-xcox)(2)as-2, iron arsenide superconductor, symmetry, transition|
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).
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