Lai Xiaofang, Liu Ying, Lü Xujie, Zhang Sijia, Bu Kejun, Jin Changqing, Zhang Hui, Lin Jianhua, Huang Fuqiang
Beijing National Laboratory for Molecular Sciences and State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Sci Rep. 2016 Aug 8;6:31077. doi: 10.1038/srep31077.
Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change of anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Finally, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS.
压力是研究铁基超导体的有力工具。在此，我们报告了新发现的超导体FeS的系统高压输运和结构表征。结果发现，超导体FeS（四方相）在0.4吉帕压力下部分转变为六方结构，然后在7.4吉帕时完全转变为正交相，最终在9.0吉帕以上转变为单斜相。四方相FeS的超导转变温度随压力逐渐降低，这与四方相FeSe的情况不同。随着压力增加，S-Fe-S键角仅略有变化，但阴离子高度偏离1.38埃更远。阴离子高度的这种变化，以及压力下的结构不稳定性，应与超导性的抑制密切相关。我们还观察到在6.0吉帕时发生异常的金属-半导体转变，以及在9.6吉帕以上进一步压缩时电阻异常增加。前者可归因于四方-正交结构相变，后者可归因于高压单斜相的电子结构变化。最后，首次绘制了四方相FeS作为压力和温度函数的相图，这将为理解超导FeS的结构和物理性质提供新的线索。
