title: Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.
abstract: Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Science , Beijing 100190, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Dong
authors.forename: Huaxue
authors.initials: H
authors.lastname: Zhou
authors.forename: Huaixin
authors.initials: H
authors.lastname: Yang
authors.forename: Jie
authors.initials: J
authors.lastname: Yuan
authors.forename: Kui
authors.initials: K
authors.lastname: Jin
authors.forename: Fang
authors.initials: F
authors.lastname: Zhou
authors.forename: Dongna
authors.initials: D
authors.lastname: Yuan
authors.forename: Linlin
authors.initials: L
authors.lastname: Wei
authors.forename: Jianqi
authors.initials: J
authors.lastname: Li
authors.forename: Xinqiang
authors.initials: X
authors.lastname: Wang
authors.forename: Guangming
authors.initials: G
authors.lastname: Zhang
authors.forename: Zhongxian
authors.initials: Z
authors.lastname: Zhao