Manifestation of hopping conductivity and granularity within phase diagrams of LaO1-x F x BiS2, Sr1-x La x FBiS2 and related BiS2-based compounds.

ABSTRACT

Layered BiS [Formula see text] -based series, such as LaO [Formula see text] F [Formula see text] BiS [Formula see text] and Sr [Formula see text] La [Formula see text] FBiS [Formula see text] , offer ideal examples for studying normal and superconducting phase diagram of a solid solution that evolves from a nonmagnetic band-insulator parent. We constructed typical [Formula see text] phase diagrams of these systems based on events occurring in thermal evolution of their electrical resistivity, [Formula see text]. Overall evolution of these diagrams can be rationalized in terms of (i) Mott-Efros-Shklovskii scenario which, within the semiconducting [Formula see text] regime ([Formula see text] metal-insulator transition), describes the doping influence on the thermally activated hopping conductivity. (ii) A granular metal (superconductor) scenario which, within [Formula see text], describes the evolution of normal and superconducting properties in terms of conductance g, Coulomb charging energy E c and Josephson coupling J; their joint influence is usually captured within a [Formula see text] phase diagram. Based on analysis of the granular character of [Formula see text], we converted the [Formula see text] diagrams into projected g - T diagrams which, being fundamental, allow a better understanding of evolution of various granular-related properties (in particular the hallmarks of normal-state [Formula see text] feature and superconductor-insulator transition) and how such properties are influenced by x, pressure or heat treatment.