PhysRevB_97_094505.pdf 779 KB
Terao, Takahiro Research Institute for Interdisciplinary Science, Okayama University
Yang, Xiaofan Research Institute for Interdisciplinary Science, Okayama University
Miao, Xiao Research Institute for Interdisciplinary Science, Okayama University
Zheng, Lu Research Institute for Interdisciplinary Science, Okayama University
Goto, Hidenori Research Institute for Interdisciplinary Science, Okayama University ORCID Kaken ID publons researchmap
Miyazaki, Takafumi Research Laboratory for Surface science, Okayama University
Yamaoka, Hitoshi RIKEN SPring-8 Center
Ishii, Hirofumi National Synchrotron Radiation Research Center
Liao, Yen-Fa National Synchrotron Radiation Research Center
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 Tc-c 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 Tc-c phase diagram is depicted using the data obtained thus far from FeSe codoped with a metal and NH3 or amine, indicating two distinct Tc-c lines below c = 17.5A° .
This is an article published by American Physical Society
This study was partly supported by Grants-in-Aid (26105004 and 26400361) from MEXT, by JST ACT-C Grant No. JPMJCR12YW, Japan, and by the Program for Promoting the Enhancement of Research Universities.
Physical Review B
American Physical Society
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