Superconductivity at 35 K by self doping in RbGd₂Fe₄As₄O₂

Abstract

We report synthesis, crystal structure and physical properties of a novel quinary compound RbGd₂Fe₄As₄O₂. The new iron oxyarsenide is isostructural to the fluo-arsenide KCa₂Fe₄As₄F₂, both of which contain separate double Fe₂As₂ layers that are self hole-doped in the stoichiometric composition. Bulk superconductivity at [Formula: see text] K is demonstrated by the measurements of electrical resistivity, dc magnetic susceptibility and heat capacity. An exceptionally high value of the initial slope of the upper critical field ([Formula: see text]d[Formula: see text]/d[Formula: see text] [Formula: see text] T K^-1) is measured for the polycrystalline sample.