TY - JOUR
T1 - Intercalant dependence of superconductivity in Ax(NH3)yFe2-δSe2 single crystals
AU - Lee, Ji Hyun
AU - Kakuto, Takeshi
AU - Ashida, Keishi
AU - Shibasaki, Seiji
AU - Kambe, Takashi
N1 - Funding Information:
We would like to thank N. Saini and T. Yokoya for stimulating discussions on local structural analysis of present materials. The X-ray diffraction patterns were partly measured in research projects (2013G668) of KEK-PF. This research was partly supported by a Grant-in-Aid for Scientific Research from the Japanese Ministry of Education, Culture, Sports, Science and Technology, Japan (23340104 and 15H03529), and the Program for Advancing Strategic International Networks to Accelerate the Circulation of Talented Researchers from JSPS.
Publisher Copyright:
© 2018 Author(s).
PY - 2018/6/1
Y1 - 2018/6/1
N2 - Metal intercalation using a solvent has produced significant advances in the development of Fe-chalcogenide superconducting materials. Recently, the superconducting transition temperature (TC) of metal-intercalated FeSe has been raised to 46 K using ammonia as the solvent for the alkali-metal atom. However, multiple superconducting phases have been found, which may arise from different concentrations of intercalants, further complicating the situation. Here, we report the synthesis of single-crystals of metal-intercalated FeSe superconductors using liquid ammonia, and their physical properties. Particularly, utilization of single-crystals allows us to investigate the resistivity in these ammoniated metal-intercalated FeSe superconductors, Ax(NH3)yFe2-δSe2, for the first time. Firstly, we compared with their TC s and the interlayer distance between the FeSe layers (dI) as a function of ionic radius (r) of the exchangeable intercalant. We found that both TC and dI show weak dependence on the r, if the r is smaller than the effective size of another intercalant, i.e., NH3 molecule. Besides the enhancement of the dI by the insertion of NH3 molecule, one expects that the charge-transfer due to the intercalation of cation would leads to the shift of the Fermi energy. The intercalants (Ba and K) have similar rs, but different valences (Ba2+ and K+), which may throw light on the significance of charge transfer. When the metal concentrations were investigated on the cleaved surfaces of these single crystals, clear differences were found between the two compounds, with the K-concentration about double the Ba-concentration, which may imply the identical charge-transfer. This was also supported for the investigation of the Li-concentration. These results suggest not only the local environment within the conductive FeSe layers but also the significance of the number of electronic charges supplied to the FeSe layers by the intercalated metal and/or ammonia molecules.
AB - Metal intercalation using a solvent has produced significant advances in the development of Fe-chalcogenide superconducting materials. Recently, the superconducting transition temperature (TC) of metal-intercalated FeSe has been raised to 46 K using ammonia as the solvent for the alkali-metal atom. However, multiple superconducting phases have been found, which may arise from different concentrations of intercalants, further complicating the situation. Here, we report the synthesis of single-crystals of metal-intercalated FeSe superconductors using liquid ammonia, and their physical properties. Particularly, utilization of single-crystals allows us to investigate the resistivity in these ammoniated metal-intercalated FeSe superconductors, Ax(NH3)yFe2-δSe2, for the first time. Firstly, we compared with their TC s and the interlayer distance between the FeSe layers (dI) as a function of ionic radius (r) of the exchangeable intercalant. We found that both TC and dI show weak dependence on the r, if the r is smaller than the effective size of another intercalant, i.e., NH3 molecule. Besides the enhancement of the dI by the insertion of NH3 molecule, one expects that the charge-transfer due to the intercalation of cation would leads to the shift of the Fermi energy. The intercalants (Ba and K) have similar rs, but different valences (Ba2+ and K+), which may throw light on the significance of charge transfer. When the metal concentrations were investigated on the cleaved surfaces of these single crystals, clear differences were found between the two compounds, with the K-concentration about double the Ba-concentration, which may imply the identical charge-transfer. This was also supported for the investigation of the Li-concentration. These results suggest not only the local environment within the conductive FeSe layers but also the significance of the number of electronic charges supplied to the FeSe layers by the intercalated metal and/or ammonia molecules.
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U2 - 10.1063/1.5022120
DO - 10.1063/1.5022120
M3 - Article
AN - SCOPUS:85048618526
SN - 2158-3226
VL - 8
JO - AIP Advances
JF - AIP Advances
IS - 6
M1 - 065213
ER -