Local-structure insight into the improved superconducting properties of Pb-substituted La(O,F)BiS2: A photoelectron holography study

Abstract Pb-substituted La(O,F)BiS₂ (Pb-LaOFBiS₂) 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. PEH study of Pb-LaOFBiS₂ 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 were observed. Across the temperature of the resistivity anomaly (T*), photoelectron holograms of Bi 4f changed. Comparison of holograms with those of non-substituted LaOFBiS₂sample, as well as simulated holograms, suggested that (1), above T*, the tetragonal structure of Pb-LaOFBiS₂ are different from the tetragonal structure of LaOFBiS₂ and (2), below T*, the tetragonal structure still remains in Pb-LaOFBiS₂. We discuss possible origin of the difference in the structure above T* and implication of the result below T*, which are necessary ingredients to understand the physical properties of Pb-LaOFBiS₂.