Paul Scherrer Institut, Swiss Light Source, Villigen PSI CH-5232, Switzerland.
Nat Commun. 2013;4:1470. doi: 10.1038/ncomms2428.
Motivated by the premise that superconductivity in iron-based superconductors is unconventional and mediated by spin fluctuations, an intense research effort has been focused on characterizing the spin-excitation spectrum in the magnetically ordered parent phases of the Fe pnictides and chalcogenides. For these undoped materials, it is well established that the spin-excitation spectrum consists of sharp, highly dispersive magnons. The fate of these high-energy magnetic modes upon sizable doping with holes is hitherto unresolved. Here we demonstrate, using resonant inelastic X-ray scattering, that optimally hole-doped superconducting Ba(0.6)K(0.4)Fe(2)As(2) retains well-defined, dispersive high-energy modes of magnetic origin. These paramagnon modes are softer than, though as intense as, the magnons of undoped antiferromagnetic BaFe(2)As(2). The persistence of spin excitations well into the superconducting phase suggests that the spin fluctuations in Fe-pnictide superconductors originate from a distinctly correlated spin state. This connects Fe pnictides to cuprates, for which, in spite of fundamental electronic structure differences, similar paramagnons are present.
受铁基超导体中超导性是非传统的，并且由自旋涨落介导这一前提的启发，人们已经投入了大量的研究精力来描述 Fe 磷化物和 chalcogenides 母体相中自旋激发谱的特征。对于这些未掺杂的材料，已经确定自旋激发谱由尖锐、高度弥散的磁振子组成。在掺杂大量空穴后，这些高能磁模式的命运迄今仍未解决。在这里，我们使用共振非弹性 X 射线散射证明，最佳掺杂空穴的超导 Ba(0.6)K(0.4)Fe(2)As(2)保留了定义明确、弥散的高能磁起源模式。这些 paramagnon 模式比未掺杂反铁磁 BaFe(2)As(2)的磁子软，但强度相当。自旋激发在超导相中持续存在表明，Fe-磷化物超导体中的自旋涨落源于明显相关的自旋态。这将 Fe 磷化物与铜酸盐联系起来，尽管在基本电子结构上存在差异，但在铜酸盐中也存在类似的 paramagnon。
