title: A study of temperature dependent local atomic displacements in a Ba(Fe(1-x)Co(x))2As2 superconductor.
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.
authors.affiliation: Dipartimento 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.
authors.forename: M Y
authors.initials: MY
authors.lastname: Hacisalihoglu
authors.affiliation: Dipartimento di Fisica, Universitá di Roma "La Sapienza", P. le Aldo Moro 2, 00185 Roma, Italy. Naurang.saini@roma1.infn.it and Center for Life NanoScience@Sapienza, Istituto Italiano di Tecnologia, V. le Regina Elena 291, 00185 Rome, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Paris
authors.affiliation: Dipartimento di Fisica, Universitá di Roma "La Sapienza", P. le Aldo Moro 2, 00185 Roma, Italy. Naurang.saini@roma1.infn.it and Elettra, Sincrotrone Trieste, Strada Statale 14, Km 163.5, Basovizza, Trieste, Italy.
authors.forename: B
authors.initials: B
authors.lastname: Joseph
authors.affiliation: ALBA Synchrotron Light Facility, Crta. BP 1413, Km. 3.3, 08290 Cerdanyola del Vallés, Barcelona, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Simonelli
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan.
authors.forename: T J
authors.initials: TJ
authors.lastname: Sato
authors.affiliation: Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Mizokawa
authors.affiliation: Dipartimento di Fisica, Universitá di Roma "La Sapienza", P. le Aldo Moro 2, 00185 Roma, Italy. Naurang.saini@roma1.infn.it.
authors.forename: N L
authors.initials: NL
authors.lastname: Saini