Type II superconductors exhibit a fascinating phenomenology that is determined by the dynamical properties of the vortex matter hosted by the material. A crucial element in this phenomenology is vortex pinning by material defects, e.g., immobilizing vortices at small drives and thereby guaranteeing dissipation-free current flow. Pinning models for vortices and other topological defects, such as domain walls in magnets or dislocations in crystals, come in two standard variants: (1) weak-collective pinning, where individual weak defects are unable to pin, while the random accumulation of many force centers within a collective pinning volume combines into an effective pin, and (2) strong pinning, where strong defects produce large vortex displacements and bistabilities that lead to pinning on the level of individual defects. The transition between strong and weak pinning is quantified by the Labusch criterion $\kappa \approx f_p/\overline{C}\xi =1$, where $f_p$ and $\overline{C}$ are the force of one defect and the effective elasticity of the vortex lattice, respectively ($\xi$ is the coherence length). Here, we show that a third generic type of pinning becomes dominant when the pinning force $f_p$ enters the weak regime, the pinning by rare events. We find that within an intermediate regime $1/2<\kappa <1$, compact pairs of weak defects define strong pinning clusters that extend the mechanism of strong pinning into the weak regime. We present a detailed analysis of this cluster-pinning mechanism and show that its pinning force density parametrically dominates over the weak pinning result. The present work is a first attempt to include correlations between defects into the discussion of strong pinning.

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罕见事件在钉扎问题中的作用

II型超导体表现出令人着迷的现象，该现象由材料所携带的涡旋物质的动力学特性决定。这种现象的一个关键因素是由于材料缺陷引起的涡流钉扎，例如，将涡流固定在小型驱动器上，从而确保无耗散的电流通过。旋涡和其他拓扑缺陷（例如磁体中的畴壁或晶体中的位错）的钉扎模型有两种标准变形：（1）弱集合钉扎，其中单个弱缺陷无法钉扎，而许多力的随机积累集中钉扎体积内的中心合并为有效钉扎，（2）强钉扎，其中强缺陷会产生大的涡旋位移和双稳性，从而导致钉扎单个缺陷的水平。$\kappa \approx F_p/\overline{C}\xi =\mathrm{1个}$，在哪里 $F_p$ 和 $\overline{C}$ 分别是一个缺陷的力和涡流晶格的有效弹性（$\xi$是相干长度）。在这里，我们显示了当钉扎力出现时，第三种通用钉扎类型将占主导地位$F_p$进入软弱的政权，由罕见的事件牵制。我们发现，在中间制度下$\mathrm{1个}/2<\kappa <\mathrm{1个}$紧致的弱缺陷对定义了强钉扎簇，这些簇将强钉扎机制扩展到了弱状态。我们对该簇钉扎机制进行了详细分析，并显示了其钉扎力密度在弱钉扎结果上在参数上占主导地位。目前的工作是将缺陷之间的相关性纳入强钉扎讨论的首次尝试。