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 (ΔTc) due to their non-bulk nature. Surprisingly, ΔTc becomes sharper or broader after an electric current larger than a threshold value (It) is applied, with a concomitant change in the normal-state magnetism. The sharpened (broadened) ΔTc 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. Clues to the superconducting behavior of a complex, iron-based substance can be revealed with a technique based on electric current. When rare-earth atoms are incorporated into calcium–iron–arsenic (CaFe2As2) crystals, simultaneous magnetic and superconductive properties emerge after cooling below 50 K. Soon-Gil Jung and Tuson Park from South Korea’s Sungkyunkwan University, Suwon, and colleagues report that passing milliamp-level electric currents through rare-earth-doped CaFe2As2 causes unexpected shifts in superconducting transition temperatures and magnetic field responses. In some samples, a sharpening of the superconductivity onset point was accompanied by a loss of magnetic signals, while in others magnetism improved at the expense of well-defined superconducting temperatures. The researchers conclude that these changes arise from inhomogeneities within doped CaFe2As2, possibly from iron magnetic states or tiny self-assembled nanocomposites that become unstable past a current threshold. Large inhomogeneous electronic states in rare-earth-doped CaFe2As2 produce striking results of manipulating the superconducting phases via current-driven magnetic state. Magnetization hysteresis loops at superconducting state (2 K) and normal state (50 K) for La-doped CaFe2As2 are largely changed by the electric current because their high-Tc regions are localized. Current path between high-Tc regions is considered as a long wire, thus current-induced large magnetic field around the path can modulate the magnetic state in normal/weak superconducting regions. These observations provide new insights into the role of Fe in the Fe-based superconductors and ideas for the design of new superconducting devices.