Critical current properties of Fe-based superconductors
The iron-based superconductors (IBSs) discovered in 2008
offer a rich playground for both fundamental and practical research on
high-critical temperature (high-Tc) superconductivity. The phase diagrams of
iron-based superconductors are complex, exhibiting a variety of orders, such as
antiferromagnetic, orbital, and possible nematic orders. Understanding the
phase diagram may be key to understanding high-Tc superconductivity. From the
application pint of view, IBSs have many out-standing properties, such as
high-Tc, ultrahigh upper critical field (Hc2), low anisotropies, making them
very promising for high-field applications.
In the present study, we pay attention to the critical current (Jc) properties of IBSs. For the BaFe2As2-based superconductors, Ba1 − xKxFe2As2, Ba(Fe1 − xCox )2As2, and BaFe2(As1 − xPx )2 , the magnitude of Jc was sharply enhanced at doping levels corresponding to the slightly underdoped to optimally doped region in these three cases irrespective of the distinct character (charge type and the substitution site) of dopants. Furthermore Jc exhibits salient in-plane anisotropy, which agrees with the normal state in-plane resistivity anisotropy. The results indicate the presence of an exotic pinning mechanism which is closely tied to the underlying electronic phase diagram.
As for the CaKFe4As4 (CaK1144) system, which is a new variation of the 122-based IBS discovered by ourselves where Ca and K atoms are regularly located in distinct layers without forming solid solution, we found that the Jc properties are distinct from other IBSs, characterized by significantly higher Jc with H//ab configuration as well as an unprecedented temperature-induced enhancement in Jc with H//c configuration. We propose a comprehensive explanation of the unusual Jc properties based on the unique intergrowths structure existing in this compound.
Host: Prof. Changyoung Kim