Manipulating superconducting phases via current-driven magnetic states in rare-earth-doped CaFe₂As₂

Inhomogeneous superconductivity in rare-earth (RE)-doped CaFe₂As₂ (Ca122) compounds leads to a novel state of matter in which the superconducting and magnetic states can be simultaneously controlled by using an electric current (I). Both La- and Ce-doped Ca122 single crystals show a very broad superconducting transition width (ΔT _c) due to their non-bulk nature. Surprisingly, ΔT _c becomes sharper or broader after an electric current larger than a threshold value (I _t) is applied, with a concomitant change in the normal-state magnetism. The sharpened (broadened) ΔT _c is accompanied by a decrease (an increase) in the amplitude of the ferromagnetic signals. The sensitive changes in the superconductivity and magnetism that occur when an external current is applied are related to the inhomogeneous electronic states that originate from the Fe magnetic state and/or self-organized superconducting/magnetic composites in Ca122 compounds. These discoveries shed new light on the role of Fe in Fe-based superconductors and will provide new ideas for the design of novel superconducting devices.