Human-Made Material Pushes the Bounds of Superconductivity

A multi-university team of researchers (University of Wisconsin-Madison, Florida State University and University of Michigan) has artificially engineered a unique multilayer material that could lead to breakthroughs in both superconductivity research and in real-world applications.

The research team engineered and measured the properties of superlattices of pnictide superconductors. A superlattice is the complex, regularly repeating geometric arrangement of atoms – its crystal structure – in layers of two or more materials. Pnictide superconductors include compounds made from any of five elements in the nitrogen family of the periodic table.

The researchers' new material is composed of 24 layers that alternate between the pnictide superconductor and a layer of the oxide strontium titanate:

(SrTiO3(1.2 nm)/Co-doped BaFe2As2 (13 nm))×24

(O- BaFe2As2 (3 nm)/Co-doped BaFe2As2 (13 nm))×24.

Creating such systems is difficult, especially when the arrangement of atoms, and chemical compatibility, of each material is very different. Yet, layer after layer, the researchers maintained an atomically sharp interface -- the region where materials meet. Each atom in each layer is precisely placed, spaced and arranged in a regularly repeating crystal structure.

The new material also has improved current-carrying capabilities. As they grew the superlattice, the researchers also added a tiny bit of oxygen to intentionally insert defects every few nanometers in the material. These defects act as vertical and planar pinning centers to immobilize tiny magnetic vortices that, as they grow in strength in large magnetic fields, can limit current flow through the superconductor. So if single-layer Co-doped BaFe2As2 has Tc = 20,5 К, Jc (4,2 K, SF) = 2,9 МА/sm2, Jc (4,2 K, 10 Т) = 0,6 МА/sm2, the appropriate parameters for superlattice (O- BaFe2As2 (3 нм)/Co-doped BaFe2As2 (13 нм))×24 are 23 К, 3,2 МА/см2, 0,3 МА/см2.

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