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A study of temperature dependent local atomic displacements in a Ba(Fe(1-x)Co(x))2As2 superconductor
M Y Hacisalihoglu1, E Paris2, B Joseph3
1Dipartimento di Fisica, Universitá di Roma "La Sapienza", P. le Aldo Moro 2, 00185 Roma, Italy. Naurang.saini@roma1.infn.it and Department of Physics, Recep Tayyip Erdogan University, 53100 Rize, Turkey and Department of Physics, Karadeniz Technical University, 61080 Trabzon, Turkey.
Abstract:
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.
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