In order to enhance the critical current density ($J_c$) of superconductors, introduction of columnar defects (CDs) through swift-particle irradiation is effective. By dispersing the direction of CDs (splayed CDs), not only further enhancement of $J_c$ has been confirmed but also an anomalous peak effect (APE) in $J_c$ at a certain magnetic field determined by the irradiation dose was observed. It has been proposed that the APE arises from the suppression of kink motion and/or the effects of vortex entanglement in systems with splayed CDs. In this study, we measure $J_c$ properties of optimally K-doped Ba-122-type iron-based superconductor Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ single crystals with splayed CDs that are introduced asymmetrically with respect to the $c$-axis by irradiating 2.6 GeV U ions. We discuss the significance of the average direction of splayed CDs to the APE. We also discuss the relationship between the APE and the entanglement of vortices.

中文翻译：

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不对称展开柱状缺陷对 Ba0.6K0.4Fe2As2 异常峰效应的影响

为了提高超导体的临界电流密度（$J_c$），通过快速粒子辐射引入柱状缺陷（CD）是有效的。通过分散CD（张开的CD）的方向，不仅证实了$J_c$的进一步增强，而且还观察到了在由辐射剂量确定的某个磁场下$J_c$的异常峰值效应（APE）。有人提出，APE 是由于抑制扭结运动和/或在具有展开 CD 的系统中涡旋纠缠的影响而产生的。在这项研究中，我们测量了最佳 K 掺杂 Ba-122 型铁基超导体 Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2} 的 $J_c$ 特性}$ 具有展开 CD 的单晶，通过照射 2.6 GeV U 离子相对于 $c$ 轴不对称地引入。我们讨论展开的 CD 的平均方向对 APE 的重要性。我们还讨论了 APE 与涡旋纠缠之间的关系。