A new iron-based superconductor, calcium-iron-platinum-arsenic, is magnetic but not superconducting at the lowest platinum concentrations and superconducting but not magnetic at the higher platinum levels; most of the other iron-based superconductors are both.This clear separation of magnetism and superconductivity in calcium-iron-platinum-arsenic lets scientists figure out what properties depend on superconductivity alone. In addition, this material exhibits the largest electronic anisotropy, meaning its properties depend on the direction in which they are measured, thus making it very attractive for comparison with high-temperature cuprate superconductors. By measuring the characteristic decay of the magnetic field at the surface of iron-arsenide superconductors, the so-called London penetration depth, researchers can determine the structure of the superconducting gap, which is necessary to understand the mechanism of superconductivity. The synthesis of high quality single crystals enabled the discovery of the universality of the London penetration depth.This research helps answer the basic question “What are the universal characteristics of iron-arsenide superconductors?”.
Doping-Dependent Superconducting Gap Anisotropy in the Two-Dimensional Pnictide Ca<sub>10</sub>(Pt<sub>3</sub>As<sub>8</sub>)[(Fe<sub>1-x</sub>Pt<sub>x</sub>)2As<sub>2</sub>]<sub>5</sub>