铁基超导体Fe_(1+y)Te_(1-x)Se_x中磁性的中子散射研究

Magnetic neutron scattering studies on the Fe-based superconductor system Fe_(1+y)Te_(1-x)Se_x

本文对本研究组主要的研究领域——利用中子散射研究铁基超导体系Fe1+yTe1-xSex中磁性与超导的相互作用进行简要综述.Fe1+yTe1-xSex具有和其他铁基、铜基超导体相似的相图——母相Fe1+yTe是反铁磁体,随着Se掺杂的增加,母相的反铁磁序受到抑制,随后在x～30%处体超导出现,在x～50%处达到最佳掺杂,此时超导转变温度Tc～15 K,达到整个体系在常压下的Tc最大值.它们的相图又存在着差别:在相图末端,即当Se掺杂达100%时,Fe1+ySe仍然超导,Tc～8 K.该体系母相磁有序的面内波矢大致为(0.5,0)(采用每个原胞含2个铁原子的四方结构),随着Se含量的增加,在超导逐渐发展的同时,磁激发谱的谱重被逐渐转移到波矢为(0.5,0.5)处.(0.5,0.5)处在温度低于Tc时出现中子-自旋共振峰.施加外磁场后,超导受到抑制,该共振峰也被压制.从这些实验结果我们得到以下的结论:在这个体系中磁性和超导紧密耦合在一起——(0.5,0)处的静态磁有序与超导互相竞争,(0.5,0.5)附近的自旋激发则可能对超导电性的形成具有重要的促进作用.本文还将简要讨论磁性的来源和3d过渡金属的替代效应.

We present a brief overview on the interplay between magnetism and superconductivity in one of the Fe-based superconductor systems, Fel＋yTel-xSex. The parent compound Fel＋yTe is an antiferromagnet; with Se doping, antifed romagnetic order is suppressed, followed by the appearance of superconductivity; optimal superconductivity is achieved when x ～ 50%, with a superconducting temperature Tc of ～ 15 K. The parent compound has an in-plane magnetic ordering wave vector around （0.5, 0） （using the tetragonal notation with two Fe atoms per cell）. As Se concentration increases, the spectral weight appears to shift to the wave vector around （0.5, 0.5）, accompanying the optimization of superconductivity. A neutron-spin resonance is observed around （0.5, 0.5） below To, and is suppressed, along with superconductivity, by an externM magnetic field. Taking these evidences into account, we conclude that magnetism and superconductivity in this system couple to each other closely--while the static magnetic order around （0.5, 0） competes with superconductivity, the spin excitations around （0.5, 0.5） may be an important ingredient for it. We also discuss the nature of magnetism and substitution e～ects of 3d transition metals.