title: The effect of RE substitution in layered REO(0.5)F(0.5)BiS2: chemical pressure, local disorder and superconductivity.
abstract: We have studied the effect of RE substitution on the structure and the local atomic disorder in REO0.5F0.5BiS2 (RE = rare-earth) to understand their correlation with the bulk superconductivity in these materials. The mean RE size, affecting the chemical pressure, has been varied in two series namely Ce1-xNdxO0.5F0.5BiS2 and Nd1-ySmyO0.5F0.5BiS2. The lattice parameters evolve anomalously, showing an anisotropic shrinkage (elongation) of the c-axis (a-axis) to an isotropic expansion of the lattice with increasing mean RE size. The Bi L3-edge extended X-ray absorption fine structure (EXAFS) measurements are performed to investigate local displacements in the BiS2 lattice, revealing a large disorder and a sharp boundary between the Ce-containing and Sm-containing series with a distinct local structure. The results suggest that the bulk superconductivity in REO0.5F0.5BiS2 is correlated with anomalous atomic displacements in the Bi-S1 network, likely to be a combined effect of active Bi 6s electronic states and a possible Jahn-Teller-like instability of the Bi 6px/6py electrons.
authors.affiliation: Department of Electrical and Electronic Engineering, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Mizuguchi
authors.forename: E
authors.initials: E
authors.lastname: Paris
authors.forename: T
authors.initials: T
authors.lastname: Sugimoto
authors.forename: A
authors.initials: A
authors.lastname: Iadecola
authors.forename: J
authors.initials: J
authors.lastname: Kajitani
authors.forename: O
authors.initials: O
authors.lastname: Miura
authors.forename: T
authors.initials: T
authors.lastname: Mizokawa
authors.forename: N L
authors.initials: NL
authors.lastname: Saini