Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first-order phase transition

Many structural phase transitions are of first order, and many superconducting transitions are of second order. Some iron-based materials have a first-order (magneto)structural phase transition and then cross over to a superconducting phase at low temperatures. Using nanoscale imaging, the authors show that this results in separated superconducting and normal regions, each showing a different crystalline structure. In systems having different crystalline phases, it can be energetically favorable to separate a superconductor into patches.