Local-structure insight into the improved superconducting properties of Pb-substituted La(O, F)BiS: a photoelectron holography study.

Pb-substituted La(O, F)BiS (Pb-LaOFBiS) exhibits improved superconducting properties and a resistivity anomaly around 100 K that is attributed to a structural transition. We have performed temperature(T)-dependent photoelectron holography (PEH) to study dopant incorporation sites and the local structure change across the anomaly. The PEH study of Pb-LaOFBiS provided evidence for the dominant incorporation sites of Pb and F: Pb atoms are incorporated into the Bi sites and F atoms are incorporated into the O site. No remarkable difference in the local structures around Pb and Bi atoms was observed. Across the temperature of the resistivity anomaly (T), photoelectron holograms of Bi 4f changed. Comparisons of holograms with those of non-substituted LaOFBiS sample, as well as simulated holograms, suggested that (1), above T, the tetragonal structure of Pb-LaOFBiS is different from the tetragonal structure of LaOFBiS and (2), below T, the tetragonal structure still remains in Pb-LaOFBiS. We discuss a possible origin of the difference in the structure above T and the implication of the result below T, which are necessary ingredients to understand the physical properties of Pb-LaOFBiS.