TY - JOUR
T1 - Asymmetrically optimized structure in a high-T c single unit-cell FeSe superconductor
AU - Fukaya, Yuki
AU - Zhou, Guanyu
AU - Zheng, Fawei
AU - Zhang, Ping
AU - Wang, Lili
AU - Xue, Qi Kun
AU - Shamoto, Shin Ichi
N1 - Funding Information:
We thank Y Yanase, T Nojima, W Higemoto and S Maekawa for discussions and I Mochizuki and T Hyodo for experimental support. This work was performed under the approval of the Photon Factory Program Advisory Committee (Proposal No. 2014S2-004). LW and Q-KX acknowledge support from NSFC (Grants No. 11574174 and No. 11774193) and MOST of China (Grant No. 2015CB921000).
Publisher Copyright:
© 2018 IOP Publishing Ltd.
PY - 2019/2/6
Y1 - 2019/2/6
N2 - We report asymmetric Se heights in a single unit-cell (UC) FeSe on SrTiO3(0 0 1) substrate with the highest superconducting transition temperature (T c) among the Fe-based superconductors revealed by total-reflection high-energy positron diffraction measurements. Among various iron-based superconductors, this single UC FeSe on the SrTiO3(0 0 1) has been the best material to achieve the highest-T c above 50 K. We found the asymmetric Se heights of 1.44 ± 0.03 and 1.33 ± 0.03 Å from the single Fe layer by the intensity analysis based on dynamical diffraction theory. The average Se height results in 1.39 ± 0.04 Å, corresponding to the optimum value for Fe-based superconductors. In addition, the average of bond angles of Se-Fe-Se, 107.2 ± 1.1 and 111.5 ± 1.2° becomes 109.3 ± 1.6°, which is close to the optimum value of 109.5° for a regular tetrahedron. Thus, this single UC FeSe is found to have asymmetrically optimized structure. Based on our first-principles calculations, the asymmetry does not change the bandwidth whereas it splits the electron bands at the M point only at the bottom. These calculations suggest that at low electron doping, the structural asymmetry is expected to lead to exotic properties of non-centrosymmetric superconductivity, whereas after a certain amount of electron doping, average anion height plays an important role for high-T c.
AB - We report asymmetric Se heights in a single unit-cell (UC) FeSe on SrTiO3(0 0 1) substrate with the highest superconducting transition temperature (T c) among the Fe-based superconductors revealed by total-reflection high-energy positron diffraction measurements. Among various iron-based superconductors, this single UC FeSe on the SrTiO3(0 0 1) has been the best material to achieve the highest-T c above 50 K. We found the asymmetric Se heights of 1.44 ± 0.03 and 1.33 ± 0.03 Å from the single Fe layer by the intensity analysis based on dynamical diffraction theory. The average Se height results in 1.39 ± 0.04 Å, corresponding to the optimum value for Fe-based superconductors. In addition, the average of bond angles of Se-Fe-Se, 107.2 ± 1.1 and 111.5 ± 1.2° becomes 109.3 ± 1.6°, which is close to the optimum value of 109.5° for a regular tetrahedron. Thus, this single UC FeSe is found to have asymmetrically optimized structure. Based on our first-principles calculations, the asymmetry does not change the bandwidth whereas it splits the electron bands at the M point only at the bottom. These calculations suggest that at low electron doping, the structural asymmetry is expected to lead to exotic properties of non-centrosymmetric superconductivity, whereas after a certain amount of electron doping, average anion height plays an important role for high-T c.
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U2 - 10.1088/1361-648X/aaf2d9
DO - 10.1088/1361-648X/aaf2d9
M3 - Article
C2 - 30523995
AN - SCOPUS:85058897370
VL - 31
JO - Journal of Physics Condensed Matter
JF - Journal of Physics Condensed Matter
SN - 0953-8984
IS - 5
M1 - 055701
ER -