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Bipartite magnetic parent phases in the iron oxypnictide superconductor

2014; Nature Portfolio; Volume: 10; Issue: 4 Linguagem: Inglês

10.1038/nphys2906

1745-2481

M. Hiraishi, Soshi Iimura, Kenji Kojima, Jun‐ichi Yamaura, Haruhiro Hiraka, Kazutaka Ikeda, Ping Miao, Yoshihisa Ishikawa, Shuki Torii, Masanori Miyazaki, Ichihiro Yamauchi, A. Koda, Kenji Ishii, Masahiro Yoshida, J. Mizuki, R. Kadono, Reiji Kumai, Takashi Kamiyama, Toshiya Otomo, Youichi Murakami, Satoru Matsuishi, Hideo Hosono,

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Superconductivity in iron pnictide compounds occurs near a magnetic phase and magnetic spin fluctuations are prime candidates for the superconducting pairing mechanism. What does this mean now that a second magnetic phase, next to another superconducting phase, is found at higher doping levels? High-temperature superconductivity appears as a consequence of doping charge carriers into an undoped parent compound exhibiting antiferromagnetic order; therefore, ground-state properties of the parent compound are highly relevant to the superconducting state1,2. On the basis of this logic, spin fluctuations have been considered as the origin of pairing of the superconducting electrons in the cuprates1. As possible pairing mechanisms, there is growing interest in unconventional spin fluctuations or advanced orbital fluctuations owing to the characteristic multi-orbital states in iron pnictides3,4,5,6. Here, we report the discovery of an antiferromagnetic phase as well as a unique structural transition in electron-overdoped LaFeAsO1−xHx (x ∼ 0.5), whereby a second parent phase is uncovered, albeit heavily doped. The unprecedented two-dome superconducting phases observed in this material can be interpreted as a consequence of the carrier doping starting from the original x ∼ 0 and additional x ∼ 0.5 parent phases towards the intermediate region7. The bipartite parent phases with distinct physical properties in the second magnetic phase provide us with an interesting example to illustrate the intimate interplay between the magnetic interaction, structural change and orbital degree of freedom in iron pnictide superconductors.