title: Emergence of double-dome superconductivity in ammoniated metal-doped FeSe.
abstract: The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tc vs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.
authors.forename: Masanari
authors.initials: M
authors.lastname: Izumi
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.
authors.forename: Lu
authors.initials: L
authors.lastname: Zheng
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Sakai
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.
authors.forename: Hidenori
authors.initials: H
authors.lastname: Goto
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.|Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.|Department of Chemistry, University of Durham, Durham DH1 3LE, UK.|Centre for Science and Technology under Extreme Conditions, Osaka University, Osaka 560-8531, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Sakata
authors.affiliation: Centre for Science and Technology under Extreme Conditions, Osaka University, Osaka 560-8531, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakamoto
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.|Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.
authors.forename: Huyen L T
authors.initials: HLT
authors.lastname: Nguyen
authors.affiliation: Centre for Science and Technology under Extreme Conditions, Osaka University, Osaka 560-8531, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Kagayama
authors.affiliation: Centre for Science and Technology under Extreme Conditions, Osaka University, Osaka 560-8531, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Shimizu
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Araki
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: Tatsuo C
authors.initials: TC
authors.lastname: Kobayashi
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kambe
authors.affiliation: Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Science, Beijing 100190, China.
authors.forename: Dachun
authors.initials: D
authors.lastname: Gu
authors.affiliation: Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Science, Beijing 100190, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Guo
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Science, Beijing 100049, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.affiliation: Institute of High Energy Physics, Chinese Academy of Science, Beijing 100049, China.
authors.forename: Yanchun
authors.initials: Y
authors.lastname: Li
authors.affiliation: Institute of Physics and Beijing National Laboratory for Condensed Matter Physics, Chinese Academy of Science, Beijing 100190, China.
authors.forename: Liling
authors.initials: L
authors.lastname: Sun
authors.affiliation: Department of Chemistry, University of Durham, Durham DH1 3LE, UK.|WPI Research Centre, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Kosmas
authors.initials: K
authors.lastname: Prassides
authors.affiliation: Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan.|Research Centre of New Functional Materials for Energy Production, Storage and Transport, Okayama University, Okayama 700-8530, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kubozono
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