The US Department of Energy’s Ames Laboratory has successfully created the first pure, single-crystal sample of a new iron arsenide superconductor, CaKFe4As4, and studies of this material have called into question some long-standing theoretical models of superconductivity.

The material is notable for having the high superconducting temperature of 35 K without the need for small amounts of additional elements (such as cobalt or nickel), called dopants. “That is important because dopants, that were previously used to induce superconductivity, also interfere with superconductivity and other important physical properties of materials” says Adam Kaminski, Ames Laboratory scientist and professor in the Department of Physics and Astronomy at Iowa State University. “This material gave us an excellent opportunity to study superconductivity in pristine samples without the interference of dopants.”

Kaminski and his fellow researchers discussed findings in an article published in Physical Review Letters. Using high-resolution, angle-resolved photoemission spectroscopy and density functional theory, the team was able to measure the superconducting gap in areas of the momentum space that were previously inaccessible in other materials and found that their results contradicted the widely accepted antiferromagnetic fluctuation model.

“Our data obtained from samples of pristine iron-arsenic superconductor represents a big deviation from previous studies of doped samples and questions some well-established theories,” says Kaminski. “It means that the predictions of previous models are only partly valid, and there are many aspects that are not completely understood. What our work has achieved is to create a new clean avenue of research, towards finding a general model to explain the behavior of these novel superconductors.”