Publikationsdatum:
2013-04-03
Beschreibung:
Nature Physics 9, 220 (2013). doi:10.1038/nphys2544 Authors: 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 Iron-based high-temperature superconductivity develops when the ‘parent’ antiferromagnetic/orthorhombic phase is suppressed, typically by introduction of dopant atoms. But their impact on atomic-scale electronic structure, although in theory rather complex, is unknown experimentally. What is known is that a strong transport anisotropy with its resistivity maximum along the crystal b axis, develops with increasing concentration of dopant atoms; this ‘nematicity’vanishes when the parent phase disappears near the maximum superconducting Tc. The interplay between the electronic structure surrounding each dopant atom, quasiparticle scattering therefrom and the transport nematicity has therefore become a pivotal focus 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)2As2 generates a dense population of identical anisotropic impurity states. Each is ∼ 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 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 and for the occurrence of the highest resistivity along the b axis.
Print ISSN:
1745-2473
Digitale ISSN:
1745-2481
Thema:
Physik
Permalink