Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals and Bose–Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions¹, glitches in pulsars², and losses in superconducting microwave circuits³, and it limits the current-carrying capacity of superconductors⁴. Understanding vortex dynamics is fundamentally and technologically important, and the competition between thermal energy and energy barriers defined by material disorder is not completely understood. Specifically, early measurements of thermally activated vortex motion (creep) in iron-based superconductors unveiled fast rates (S) comparable to measurements of YBa ₂Cu₃O_7−δ (refs 5,6,7,8,9,10). This was puzzling because S is thought to somehow correlate with the Ginzburg number (Gi), and Gi is significantly lower in most iron-based superconductors than in YBa ₂Cu₃O_7−δ. Here, we report very slow creep in BaFe ₂(As_0.67P_0.33)₂ films, and propose the existence of a universal minimum realizable S ∼ Gi^1/2(T/T_c) (T_c is the superconducting transition temperature) that has been achieved in our films and few other materials, and is violated by none. This limitation provides new clues about designing materials with slow creep and the interplay between material parameters and vortex dynamics.

超导体是研究旋涡，超流体中出现的拓扑激发，液晶和玻色-爱因斯坦凝聚物的极佳试验台。涡旋运动可能具有破坏性。它会引起相变¹，脉冲星^2的毛刺以及超导微波电路^3的损耗，并且会限制超导体⁴的载流能力。理解涡旋动力学从根本上和技术上都很重要，并且对热能和由物质无序定义的能垒之间的竞争还没有完全了解。具体而言，铁基超导体中热活化涡旋运动（蠕变）的早期测量揭示了快速速率（S）相当于YBa ₂ Cu ₃ O _{7− δ的}测量值（参考文献5,6,7,8,9,10）。之所以令人困惑，是因为人们认为S与吉恩斯堡数（Gi）相关，并且在大多数铁基超导体中，Gi明显低于YBa ₂ Cu ₃ O _{7− δ}。在这里，我们在钡铁氧体报告非常缓慢蠕变₂（如_0.67 P _0.33）_2层薄膜，并提出一种通用的最小可实现的存在小号 〜 GI ^1/2（Ť / Ť _Ç）（Ť_c是在我们的薄膜和其他几种材料中已经达到的超导转变温度，没有任何违反。这种限制为设计慢蠕变的材料以及材料参数和涡旋动力学之间的相互作用提供了新的线索。