Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1-xCox)2As2
Anisotropic impurity states, quasiparticle scattering and nematic transport in underdoped Ca(Fe1-xCox)2As2
复制标题
DOI：
10.1038/nphys2544
复制
发表时间：
2013-04-01
期刊：
影响因子：
19.6
通讯作者：
Davis, J. C.
中科院分区：
文献类型：
--
作者：
Allan, M. P.;Chuang, T-M.;Davis, J. C.
当“母体”反铁磁性/正交相被抑制时，通常通过引入掺杂原子(1)，铁基高温超导性就会产生。但是它们对原子尺度的电子结构的影响，尽管在理论上相当复杂（2-13），在实验上是未知的。已知的是，随着掺杂原子浓度的增加，强输运各向异性（14-25）随着晶体b轴（14-25）的电阻率最大而发展（14,20-25）；当母相在最大超导温度附近消失时，这种“向列性”就消失了。因此，每个掺杂原子周围的电子结构、准粒子散射和输运向列性之间的相互作用已成为研究这些材料的关键焦点（7,8,12,22,23）。在这里，通过直接可视化原子尺度的电子结构，我们发现在欠掺杂的Ca(Fe1-xCox)(2)As-2中，用Co取代Fe原子会产生密度相同的各向异性杂质态。每一个都类似于8个Fe-Fe单元格的长度，并且都是随机分布的，但都与反铁磁性的a轴对齐。通过对其周围干涉图案的成像，我们进一步证明了这些杂质态以高度各向异性的方式散射准粒子，最大散射速率集中在b轴上。这些数据直接支持了最近的建议（7,8,12,22,23），即主要是由掺杂诱导的杂质态的各向异性散射产生输运向列性；它们也对向列性与掺杂密度成正比的增强（14,20-25）和b轴上电阻率最高的出现（14-25）给出了简单的解释。
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).