Department of Physics, University of Tokyo, Tokyo, Japan.
Proc Natl Acad Sci U S A. 2011 Jul 26;108(30):12238-42. doi: 10.1073/pnas.1100102108. Epub 2011 Jul 11.
An ordered phase showing remarkable electronic anisotropy in proximity to the superconducting phase is now a hot issue in the field of high-transition-temperature superconductivity. As in the case of copper oxides, superconductivity in iron arsenides competes or coexists with such an ordered phase. Undoped and underdoped iron arsenides have a magnetostructural ordered phase exhibiting stripe-like antiferromagnetic spin order accompanied by an orthorhombic lattice distortion; both the spin order and lattice distortion break the tetragonal symmetry of crystals of these compounds. In this ordered state, anisotropy of in-plane electrical resistivity is anomalous and difficult to attribute simply to the spin order and/or the lattice distortion. Here, we present the anisotropic optical spectra measured on detwinned BaFe(2)As(2) crystals with light polarization parallel to the Fe planes. Pronounced anisotropy is observed in the spectra, persisting up to an unexpectedly high photon energy of about 2 eV. Such anisotropy arises from an anisotropic energy gap opening below and slightly above the onset of the order. Detailed analysis of the optical spectra reveals an unprecedented electronic state in the ordered phase.
在高温超导领域，临近超导相出现具有显著电子各向异性的有序相是一个热点问题。与铜氧化物的情况一样，铁砷化物中的超导性与这种有序相竞争或共存。未掺杂和欠掺杂的铁砷化物具有磁结构有序相，表现为条纹状反铁磁自旋序伴随着正交晶格畸变；自旋序和晶格畸变都打破了这些化合物晶体的四方对称性。在这个有序状态下，面内电阻率的各向异性是异常的，很难简单地归因于自旋序和/或晶格畸变。在这里，我们展示了在与 Fe 平面平行的光偏振方向上测量的脱孪晶 BaFe(2)As(2)晶体的各向异性光学光谱。在光谱中观察到明显的各向异性，一直持续到高达约 2 eV 的意外高光子能量。这种各向异性是由在有序相开始出现时下方和稍上方的各向异性能隙打开引起的。对光学光谱的详细分析揭示了有序相中的一种前所未有的电子态。
