Hacisalihoglu M Y, Paris E, Joseph B, Simonelli L, Sato T J, Mizokawa T, Saini N L
Dipartimento di Fisica, Universitá di Roma "La Sapienza", P. le Aldo Moro 2, 00185 Roma, Italy.
ALBA Synchrotron Light Facility, Crta. BP 1413, Km. 3.3, 08290 Cerdanyola del Vallés, Barcelona, Spain.
Phys Chem Chem Phys. 2016 Apr 7;18(13):9029-35. doi: 10.1039/c5cp07985c.
We have studied the local structure of a Ba(Fe(1-x)Co(x))2As2 superconductor using temperature dependent extended X-ray absorption fine structure (EXAFS) measurements. Polarized EXAFS at the Fe K-edge on an optimally doped (x = 0.06) single crystal has permitted us to determine atomic displacements across the superconducting transition temperature (T(c)). The Fe-As bondlength hardly shows any change with temperature; however, the Fe-Fe sublattice reveals a sharp anomaly across T(c), indicated by a significant drop in mean square relative displacements, similar to the one known for cuprates and A15-type superconductors. We have also found a large atomic disorder around the substituted Co, revealed by polarized Co K-edge EXAFS measurements. The Co-Fe/Co bonds are more flexible than the Fe-Fe bonds with the As-height in Co-containing tetrahedra being larger than the one in FeAs4. The results suggest that the local Fe-Fe bondlength fluctuations and the atomic disorder in this sub-lattice should have some important role in the superconductivity of Ba(Fe(1-x)Co(x))2As2 pnictides.
我们使用与温度相关的扩展X射线吸收精细结构（EXAFS）测量方法，研究了Ba(Fe(1-x)Co(x))2As2超导体的局部结构。在最佳掺杂（x = 0.06）的单晶上进行的Fe K边偏振EXAFS测量，使我们能够确定跨越超导转变温度（T(c)）的原子位移。Fe-As键长几乎不随温度变化；然而，Fe-Fe亚晶格在T(c)处显示出明显的异常，表现为均方相对位移显著下降，这与铜酸盐和A15型超导体中已知的情况类似。我们还通过偏振Co K边EXAFS测量发现，取代的Co周围存在较大的原子无序。Co-Fe/Co键比Fe-Fe键更具灵活性，含Co四面体中的As高度大于FeAs4中的As高度。结果表明，局部Fe-Fe键长波动和该亚晶格中的原子无序在Ba(Fe(1-x)Co(x))2As2磷化物的超导性中应起着重要作用。
