Cheng Wang, Lin Hai, Shen Bing, Wen Hai-Hu
Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures and Department of Physics, National Center of Microstructures and Quantum Manipulation, Nanjing University, Nanjing 210093, China.
Center for Superconducting Physics and Materials, National Laboratory of Solid State Microstructures and Department of Physics, National Center of Microstructures and Quantum Manipulation, Nanjing University, Nanjing 210093, China.
Sci Bull (Beijing). 2019 Jan 30;64(2):81-90. doi: 10.1016/j.scib.2018.12.024. Epub 2018 Dec 30.
We investigate the vortex dynamics in two typical hole doped iron based superconductors CaKFeAs (CaK1144) and BaKFeAs (BaK122) with similar superconducting transition temperatures. It is found that the magnetization hysteresis loop exhibits a clear second peak effect in BaK122 in wide temperature region while it is absent in CaK1144. However, a second peak effect of critical current density versus temperature is observed in CaK1144, which is however absent in BaK122. The different behaviors of second peak effect in BaK122 and CaK1144 may suggest distinct origins of vortex pinning in different systems. Magnetization and its relaxation have also been measured by using dynamical and conventional relaxation methods for both systems. Analysis and comparison of the two distinct systems show that the vortex pinning is stronger and the critical current density is higher in BaK122 system. It is found that the Maley's method can be used and thus the activation energy can be determined in BaK122 by using the time dependent magnetization in wide temperature region, but this is not applicable in CaK1144 system. Finally we present the different regimes with distinct vortex dynamics in the field-temperature diagram for the two systems.
我们研究了具有相似超导转变温度的两种典型空穴掺杂铁基超导体CaKFeAs（CaK1144）和BaKFeAs（BaK122）中的涡旋动力学。发现在宽温度范围内，BaK122的磁化滞后回线呈现出明显的第二峰效应，而CaK1144中则不存在。然而，在CaK1144中观察到了临界电流密度与温度的第二峰效应，而BaK122中则不存在。BaK122和CaK1144中第二峰效应的不同行为可能表明不同体系中涡旋钉扎的起源不同。还使用动态和传统弛豫方法对这两个体系进行了磁化及其弛豫的测量。对这两个不同体系的分析和比较表明，BaK122体系中的涡旋钉扎更强，临界电流密度更高。发现可以使用马利方法，因此可以通过在宽温度范围内使用随时间变化的磁化来确定BaK122中的激活能，但这不适用于CaK1144体系。最后，我们给出了这两个体系在场-温度图中具有不同涡旋动力学的不同区域。
