A member of the complex family of iron-based superconductors has been newly synthesized, shown to be highly ordered, and exhibits nearly optimal properties. Well-ordered, single crystals of CaKFe4As4 superconductors have allowed researchers to remove one of the veils of complexity for iron-based superconductors—disorder. Previously, our understanding of the higher transition temperatures, and promising high-magnetic field properties of iron-based superconductors has been associated with compounds with significant chemical disorder, making it hard to deconvolute the effects of doping and structure with their intrinsic properties. The single crystals of CaKFe4As4 have shown exceptionally large upper critical fields (in excess of 65 T) as well as high superconducting temperature values (35 K), intrinsic to ordered members of this class of compounds. Anisotropic, structural, thermodynamic and transport measurements showed the high upper critical fields and also provide the basis for additional understanding of the origins of superconductivity in this family of compounds. This ordered analogue, with optimal doping, will further aid in unraveling complexities arising from chemical and structural disorder.
The anisotropic upper critical field as a function of temperature for a stoichiometric single crystal.
Anisotropic Thermodynamic and Transport Properties of Single Crystalline CaKFe4As4