标题： 磁控涡旋动力学在铁磁超导体中 显示英文标题

标题： Magnetically-controlled Vortex Dynamics in a Ferromagnetic Superconductor

摘要： 铁磁超导体非常罕见，因为强铁磁交换场通常会破坏单态超导性。 EuFe$_2$(As$_{1-x}$P$_x$)$_2$是一种以最大临界温度为$\sim$25 K 的铁基超导体，是一种在低于$T_\mathrm{FM} \approx 19$ K 时表现出与铁磁序完全共存的独特材料。这两种序之间的相互作用导致在较高温度下铁磁畴的缩小以及在较低温度下涡旋/反涡旋的自发成核。 在这里，我们展示了如何通过施加磁场中的磁结构直接控制超导涡旋动力学。 在$T_\mathrm{FM}$以下，我们在矫顽力和蠕动激活能中都观察到显著的温度依赖峰，后者在大施加磁场中迅速被抑制。 我们将这种行为归因于自由涡旋和磁条纹畴之间独特相互作用形成的涡旋极化子。 我们提出了一个关于涡旋极化子特性的理论描述，解释了我们的主要观察结果，说明它们如何导致涡旋捕获以及短距离内的吸引涡旋-涡旋相互作用。 截然相反，在低温下的强磁不可逆性与由近畴壁处涡旋-反涡旋湮灭的激活势垒上的巨通量蠕动所控制的临界电流有关。 我们的工作揭示了磁增强涡旋钉扎的新未探索途径，特别是在高磁场下运行的高电流导体中有特别重要的应用。 显示英文摘要

摘要： Ferromagnetic superconductors are exceptionally rare because the strong ferromagnetic exchange field usually destroys singlet superconductivity. EuFe$_2$(As$_{1-x}$P$_x$)$_2$, an iron-based superconductor with a maximum critical temperature of $\sim$25 K, is a unique material that exhibits full coexistence with ferromagnetic order below $T_\mathrm{FM} \approx 19$ K. The interplay between the two leads to a narrowing of ferromagnetic domains at higher temperatures and the spontaneous nucleation of vortices/antivortices at lower temperatures. Here we demonstrate how the underlying magnetic structure directly controls the superconducting vortex dynamics in applied magnetic fields. Just below $T_\mathrm{FM}$ we observe a pronounced temperature-dependent peak in both the coercivity and the creep activation energy, the latter becoming rapidly suppressed in large applied magnetic fields. We attribute this behaviour to the formation of vortex polarons arising from the unique interaction between free vortices and magnetic stripe domains. We present a theoretical description of the properties of vortex polarons that explains our main observations, showing how they lead to vortex trapping and an attractive vortex-vortex interaction at short distances. In stark contrast, strong magnetic irreversibility at low temperatures is linked to a critical current governed by giant flux creep over an activation barrier for vortex-antivortex annihilation near domain walls. Our work reveals unexplored new routes for the magnetic enhancement of vortex pinning with particularly important applications in high-current conductors for operation at high magnetic fields.