Pressure dependence of superconductivity in low- and high-Tc phases of (NH3)yNaxFeSe

Takahiro Terao, Xiaofan Yang, Xiao Miao, Lu Zheng, Hidenori Goto, Takafumi Miyazaki, Hitoshi Yamaoka, Hirofumi Ishii, Yen-Fa Liao, and Yoshihiro Kubozono
Phys. Rev. B 97, 094505 – Published 9 March 2018

Abstract

We prepared two superconducting phases, which are called ‘‘low-Tc phase’’ and ‘‘high-Tc phase’’ of (NH3)yNaxFeSe showing Tc’s of 35 and 44 K, respectively, at ambient pressure, and studied the superconducting behavior and structure of each phase under pressure. The Tc of the 35 K at ambient pressure rapidly decreases with increasing pressure up to 10 GPa, and it remains unchanged up to 22 GPa. Finally, superconductivity was not observed down to 1.4 K at 29 GPa, i.e., Tc<1.4K. The Tc of the 44 K phase also shows a monotonic decrease up to 15 GPa and it weakly decreases up to 25 GPa. These behaviors suggest no pressure-driven high-Tc phase (called ‘‘SC-II’’) between 0 and 25 GPa for the low-Tc and high-Tc phases of (NH3)yNaxFeSe, differing from the behavior of (NH3)yCsxFeSe, which has a pressure-driven high-Tc phase (SC-II) in addition to the superconducting phase (SC-I) observed at ambient and low pressures. The Tcc phase diagram for both low-Tc and high-Tc phases shows that the Tc can be linearly scaled with c (or FeSe plane spacing), where c is a lattice constant. The reason why a pressure-driven high-Tc phase (SC-II) was found for neither low-Tc nor high-Tc phases of (NH3)yNaxFeSe is fully discussed, suggesting a critical c value as the key to forming the pressure-driven high-Tc phase (SC-II). Finally, the precise Tcc phase diagram is depicted using the data obtained thus far from FeSe codoped with a metal and NH3 or amine, indicating two distinct Tcc lines below c=17.5Å.

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  • Received 11 November 2017
  • Revised 23 January 2018

DOI:https://doi.org/10.1103/PhysRevB.97.094505

©2018 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Takahiro Terao1, Xiaofan Yang1, Xiao Miao1, Lu Zheng1, Hidenori Goto1, Takafumi Miyazaki2, Hitoshi Yamaoka3, Hirofumi Ishii4, Yen-Fa Liao4, and Yoshihiro Kubozono1,*

  • 1Research Institute for Interdisciplinary Science, Okayama University, Okayama 700–8530, Japan
  • 2Research Laboratory for Surface science, Okayama University, Okayama 700–8530, Japan
  • 3RIKEN SPring-8 Center, Hyogo 679–5148, Japan
  • 4National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan

  • *Corresponding author: kubozono@cc.okayama-u.ac.jp

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Vol. 97, Iss. 9 — 1 March 2018

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