How current flows through iron-based superconductors is very sensitive to composition. Iron-based superconductors provide a unique window into the role magnetism plays in superconductivity, because their magnetism and superconductivity coexist, whereas in conventional superconductors they do not. Researchers studied current flow by measuring the resistivity along various directions of barium-potassium-iron-arsenide superconductors with differing amounts of potassium. Samples with lower amounts of potassium exhibit electric current flow that is easier in one direction, and as the amount of potassium increases the current flow becomes harder. Surprisingly, above a certain amount of potassium, the electric current flow actually becomes easier again, but in a direction perpendicular to that for the lower amounts of potassium. This change can only be explained if the underlying magnetic behavior is intimately tied to superconductivity. Understanding the fundamental science behind high temperature superconductors lays the foundation for producing new energy saving materials.
E. C. Blomberg, M. A. Tanatar, R. M. Fernandes, I. I. Mazin, Bing Shen, Hai-Hu Wen, M. D. Johannes, J. Schmalian, and R. Prozorov, "Sign-Reversal of the In-Plane Resistivity Anisotropy in Hole-Doped Iron Pnictides," Nature Communications, 2013, 4, 1914.