Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, Stuttgart D-70569, Germany.
Nat Commun. 2011;2:219. doi: 10.1038/ncomms1223.
One of the central tenets of conventional theories of superconductivity, including most models proposed for the recently discovered iron-pnictide superconductors, is the notion that only electronic excitations with energies comparable to the superconducting energy gap are affected by the transition. Here, we report the results of a comprehensive spectroscopic ellipsometry study of a high-quality crystal of superconducting Ba₀.₆₈K₀.₃₂Fe₂As₂ that challenges this notion. We observe a superconductivity-induced suppression of an absorption band at an energy of 2.5 eV, two orders of magnitude above the superconducting gap energy 2Δ≈20 meV. On the basis of density functional calculations, this band can be assigned to transitions from As-p to Fe-d orbitals crossing the Fermi level. We identify a related effect at the spin-density wave transition in parent compounds of the 122 family. This suggests that As-p states deep below the Fermi level contribute to the formation of the superconducting and spin-density wave states in the iron arsenides.
传统超导理论的核心原则之一，包括最近发现的铁磷族超导体的大多数模型，是只有能量与超导能隙相当的电子激发才会受到相变的影响。在这里，我们报告了对高质量超导 Ba₀.₆₈K₀.₃₂Fe₂As₂晶体的全面光谱椭圆光度法研究结果，该结果对这一观点提出了挑战。我们观察到超导性诱导的 2.5eV 能量处吸收带的抑制，这比超导能隙 2Δ≈20meV 高出两个数量级。基于密度泛函计算，可以将该能带分配给穿过费米能级的 As-p 到 Fe-d 轨道的跃迁。我们在 122 族母体化合物的自旋密度波转变中发现了一个相关的效应。这表明费米能级以下很深的 As-p 态对铁砷化物中超导态和自旋密度波态的形成有贡献。
