title: Re-emerging superconductivity at 48 kelvin in iron chalcogenides.
abstract: Pressure has an essential role in the production and control of superconductivity in iron-based superconductors. Substitution of a large cation by a smaller rare-earth ion to simulate the pressure effect has raised the superconducting transition temperature T(c) to a record high of 55 K in these materials. In the same way as T(c) exhibits a bell-shaped curve of dependence on chemical doping, pressure-tuned T(c) typically drops monotonically after passing the optimal pressure. Here we report that in the superconducting iron chalcogenides, a second superconducting phase suddenly re-emerges above 11.5 GPa, after the T(c) drops from the first maximum of 32 K at 1 GPa. The T(c) of the re-emerging superconducting phase is considerably higher than the first maximum, reaching 48.0-48.7 K for Tl(0.6)Rb(0.4)Fe(1.67)Se(2), K(0.8)Fe(1.7)Se(2) and K(0.8)Fe(1.78)Se(2).
authors.affiliation: Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Liling
authors.initials: L
authors.lastname: Sun
authors.forename: Xiao-Jia
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authors.lastname: Chen
authors.forename: Jing
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authors.lastname: Guo
authors.forename: Peiwen
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authors.lastname: Gao
authors.forename: Qing-Zhen
authors.initials: QZ
authors.lastname: Huang
authors.forename: Hangdong
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authors.lastname: Wang
authors.forename: Minghu
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authors.lastname: Fang
authors.forename: Xiaolong
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authors.forename: Dachun
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authors.forename: Xiaoli
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authors.forename: Lin
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authors.lastname: Wang
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authors.lastname: Yang
authors.forename: Aiguo
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authors.lastname: Li
authors.forename: Xi
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authors.lastname: Dai
authors.forename: Ho-kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Zhongxian
authors.initials: Z
authors.lastname: Zhao