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Chin. Phys. B, 2021, Vol. 30(10): 107402    DOI: 10.1088/1674-1056/ac1f09

Superconductivity at 44.4 K achieved by intercalating EMIM+ into FeSe

Jinhua Wang(王晋花), Qing Li(李庆), Wei Xie(谢威), Guanyu Chen(陈冠宇), Xiyu Zhu(祝熙宇), and Hai-Hu Wen(闻海虎)
Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures and Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Abstract  Superconductivity with transition temperature Tc above 40 K was observed in protonated FeSe (Hy-FeSe) previously with the ionic liquid EMIM-BF4 used in the electrochemical process. However, the real superconducting phase is not clear until now. And detailed structural, magnetization, and electrical transport measurements are lacking. By using similar protonating technique on FeSe single crystals, we obtain superconducting samples with Tc above 40 K. We show that the obtained superconducting phase is not Hy-FeSe but actually an organic-ion (C6H11N2+ referred to as EMIM+)-intercalated phase (EMIM)xFeSe. By using x-ray diffraction technique, two sets of index peaks corresponding to different c-axis lattice constants are detected in the obtained samples, which belong to the newly formed phase of intercalated (EMIM)xFeSe and the residual FeSe, respectively. The superconductivity of (EMIM)xFeSe with Tc of 44.4 K is confirmed by resistivity and magnetic susceptibility measurements. Temperature dependence of resistivity with different applied magnetic fields reveals that the upper critical field Hc2 is quite high, while the irreversibility field Hirr is suppressed quickly with increasing temperature till about 20 K. This indicates that the resultant compound has a high anisotropy with a large spacing between the FeSe layers.
Keywords:  FeSe      iron-based superconductor      electrochemical intercalation  
Received:  12 July 2021      Revised:  11 August 2021      Accepted manuscript online:  19 August 2021
PACS:  74.70.Xa (Pnictides and chalcogenides)  
  74.25.-q (Properties of superconductors)  
  74.72.Ek (Electron-doped)  
  82.45.Aa (Electrochemical synthesis)  
Fund: Project supported by the National Natural Science Foundation of China (Grant Nos. 12061131001 and 52072170) and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB25000000).
Corresponding Authors:  Xiyu Zhu     E-mail:;

Cite this article: 

Jinhua Wang(王晋花), Qing Li(李庆), Wei Xie(谢威), Guanyu Chen(陈冠宇), Xiyu Zhu(祝熙宇), and Hai-Hu Wen(闻海虎) Superconductivity at 44.4 K achieved by intercalating EMIM+ into FeSe 2021 Chin. Phys. B 30 107402

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