Pressure-induced second high-T_c superconducting phase in the organic-ion-intercalated (CTA)_0.3FeSe single crystal

¹ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences Beijing 100190, China
² School of Physical Sciences, University of Chinese Academy of Sciences - Beijing 100190, China
³ Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, and CAS Key Laboratory of Strongly- coupled Quantum Matter Physics, University of Science and Technology of China Hefei, Anhui 230026, China
⁴ Institute for Solid State Physics, University of Tokyo - 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
⁵ Collaborative Innovation Center of Advanced Microstructures, Nanjing University - Nanjing 210093, China
⁶ Songshan Lake Materials Laboratory - Dongguan, Guangdong 523808, China

^(a) chenxh@ustc.edu.cn (corresponding author)
^(b) jgcheng@iphy.edu.cn (corresponding author)

Received: 21 April 2020
Accepted: 17 June 2020

Abstract

Whether the pressure-induced second high- superconducting phase (SC-II) is a universal phenomenon among the intercalated FeSe-derived superconductors deserves further investigations. Here, we report a high-pressure ac magnetic susceptibility study on the newly synthesized organic-ion-intercalated (CTA)_0.3 FeSe single crystal, which has a high at ambient pressure. We found that the superconducting transition is quickly suppressed to below 20 K upon increasing pressure to , above which the SC-II phase emerges and its increases gradually to a maximum of ca. 40 K at 5 GPa. For , both and the superconducting volume decline quickly, presumably due to the collapse of the hybrid structure against the higher pressure. Nevertheless, our results indeed evidenced the pressure-induced SC-II phase in (CTA)_0.3 FeSe, in reminiscent of the situations observed in (Li,Fe)OHFeSe and Li_0.36 (NH₃)_y Fe₂Se₂. These results thus demonstrate that pressure-induced SC-II phase should be a universal phenomenon in the electron-doped intercalated FeSe-based superconductors.