Asymmetrically optimized structure in a high-T-c single unit-cell FeSe superconductor
Asymmetrically optimized structure in a high-T-c single unit-cell FeSe superconductor
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高 T-c 单胞 FeSe 超导体的不对称优化结构
DOI：
10.1088/1361-648x/aaf2d9
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Shamoto Shin-ichi
中科院分区：
文献类型：
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作者：
Fukaya Yuki;Zhou Guanyu;Zheng Fawei;Zhang Ping;Wang Lili;Xue Qi-Kun;Shamoto Shin-ichi
本文报道了用全反射高能正电子衍射测量铁基超导体中超导转变温度(TC)最高的单晶格(UC)FeSe的非对称Se高度。在各种铁基超导体中，这种生长在SrTiO3(0 0 1)上的UCFeSe是最好的超导体，其Tc最高可达5 0K以上。通过基于动力学衍射理论的强度分析，得到了单层Fe的不对称Se高度分别为1.44±0.0 3和1.33±0.0 3。平均Se高度为1.39±0.04？，相当于铁基超导体的最佳值。此外，Se-Fe-Se的平均键角分别为107.2±1.1和111.5±1.2，为109.3±1.6，接近正四面体的最佳值109.5。因此，发现这种单一的UC FeSe具有不对称的优化结构。根据我们的第一性原理计算，这种不对称性并没有改变带宽，但它只在底部分裂了M点的电子能带。这些计算表明，在低电子掺杂时，结构不对称性有望导致非中心对称超导电性的奇特性质，而在一定量的电子掺杂后，平均阴离子高度对高T_c起重要作用。
We report asymmetric Se heights in a single unit-cell (UC) FeSe on SrTiO 3 (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 SrTiO 3 (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.