Symmetry-breaking orbital anisotropy observed for detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition
Symmetry-breaking orbital anisotropy observed for detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition
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DOI：
10.1073/pnas.1015572108
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发表时间：
2011-04-26
影响因子：
11.1
通讯作者：
Shen, Zhi-Xun
中科院分区：
文献类型：
--
作者：
Yi, Ming;Lu, Donghui;Shen, Zhi-Xun
向列性，定义为旋转对称性的破缺，最近在铜高温超导体中接近超导相的竞争相中被观察到。同样地，新的铁基高温超导体在未掺杂的母化合物中表现出四方向正交结构转变（即C-4对称性的破坏），这种转变要么先于共线自旋密度波（SDW）转变，要么与之同时发生，当这两种转变都被掺杂抑制时，就会产生超导性。中子散射、扫描隧道显微镜和输运测量已经报道了这类化合物在SDW状态中具有强的面内各向异性的证据。在这里，我们提出了一个角度分辨的光电发射光谱研究的代表性家族的电子掺杂铁砷超导体，Ba(Fe1-xCox)(2)As-2在欠掺杂区域的双晶单晶。通过应用平面内单轴应力确定晶体，从而可以测量正交态的单畴电子结构。在低温下，我们的结果清楚地显示了平面内电子各向异性，其特征是两个正交带的能量分裂很大，主要是d（xz）和d（yz）特征，这与其他探针观察到的各向异性一致。对于结构转变（T-S）先于磁转变（T-SDW）的成分x > 0，观察到T-SDW以上出现各向异性分裂，表明其与T-S特别相关。对于非应力晶体，在接近T-S时观察到能带分裂，而对于应力晶体，在相当高的温度下观察到能带分裂，揭示了电子结构中惊人的面内向列磁化率的存在。
Nematicity, defined as broken rotational symmetry, has recently been observed in competing phases proximate to the superconducting phase in the cuprate high-temperature superconductors. Similarly, the new iron-based high-temperature superconductors exhibit a tetragonal-to-orthorhombic structural transition (i.e., a broken C-4 symmetry) that either precedes or is coincident with a collinear spin density wave (SDW) transition in undoped parent compounds, and superconductivity arises when both transitions are suppressed via doping. Evidence for strong in-plane anisotropy in the SDW state in this family of compounds has been reported by neutron scattering, scanning tunneling microscopy, and transport measurements. Here, we present an angle-resolved photoemission spectroscopy study of detwinned single crystals of a representative family of electron-doped iron-arsenide superconductors, Ba(Fe1-xCox)(2)As-2 in the underdoped region. The crystals were detwinned via application of in-plane uniaxial stress, enabling measurements of single domain electronic structure in the orthorhombic state. At low temperatures, our results clearly demonstrate an in-plane electronic anisotropy characterized by a large energy splitting of two orthogonal bands with dominant d(xz) and d(yz) character, which is consistent with anisotropy observed by other probes. For compositions x > 0, for which the structural transition (T-S) precedes the magnetic transition (T-SDW), an anisotropic splitting is observed to develop above T-SDW, indicating that it is specifically associated with T-S. For unstressed crystals, the band splitting is observed close to T-S, whereas for stressed crystals, the splitting is observed to considerably higher temperatures, revealing the presence of a surprisingly large in-plane nematic susceptibility in the electronic structure.