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singlet超导性。 EuFe$_2$(As$_{1-x}$P$_x$)$_2$，一种铁基超导体，具有最高25K的临界温度，独特地在低于$T_\mathrm{FM}$ $\simeq$ $19$ K时与铁磁序完全共存。这种相互作用导致在较高温度下铁磁畴的变窄，在较低温度下自发产生涡旋/反涡旋。 在这里，我们展示了基础磁结构如何控制在施加磁场中的超导涡流动力学。 在$T_\mathrm{FM}$附近，我们观察到蠕变活化能有显著的峰值，磁力显微镜测量揭示了非常接近的 ($w\ll \lambda$) 磁通涡旋团簇的存在。我们将这些观察归因于涡旋极化子的形成，并为此提供了一个理论描述。相比之下，我们将低温下的强磁性不可逆性与由临界电流联系起来，该电流受巨磁蠕变的影响，跨越涡旋-反涡旋湮灭的势垒，这发生在畴壁附近。我们的工作提出了磁性增强涡旋钉扎的新途径，在高电流导体中有重要的应用。 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 25 K, uniquely exhibits full coexistence with ferromagnetic order below $T_\mathrm{FM}$ $\simeq$ $19$ K. The interplay leads to narrowing of ferromagnetic domains at higher temperatures and spontaneous nucleation of vortices/antivortices at lower temperatures. Here we demonstrate how the underlying magnetic structure controls the superconducting vortex dynamics in applied magnetic fields. Just below $T_\mathrm{FM}$ we observe a pronounced peak in the creep activation energy, and magnetic force microscopy measurements reveal the presence of very closely-spaced ($w\ll \lambda$) vortex clusters. We attribute these observations to the formation of vortex polarons for which we present a theoretical description. In contrast, we link strong magnetic irreversibility at low temperatures to a critical current governed by giant flux creep over an activation barrier for vortex-antivortex annihilation near domain walls. Our work suggests new routes for the magnetic enhancement of vortex pinning with important applications in high-current conductors.