AI 中文总结
研究近邻诱导超导体中自发涡旋，采用近邻耦合超导纳米复合材料及扫描超导量子干涉器件显微镜测量，观察到不同特性涡旋，其场分布更复杂，穿透深度约1至10微米，为相变早期局部相位差提供见解。
AI 中文摘要
观察自发对称性破缺对于理解从无序系统到有序系统的连续二阶相变至关重要，这通常会导致拓扑缺陷形成。在超导体中，此类拓扑缺陷被视为量子化涡旋。然而，其几何特征尚未得到充分研究和理解。对于自发涡旋成像，我们采用近邻耦合超导纳米复合材料。通过扫描超导量子干涉器件显微镜测量表明，尤其在近零场条件下，随机观察到具有不同极性、大小和形状的涡旋。自发涡旋的场分布比场诱导的阿布里科索夫涡旋更扩展、更复杂，穿透深度在约1至约10微米范围内。自发涡旋在冷却过程中因约瑟夫森耦合和热相位波动的竞争而产生，这两者在该近邻耦合系统中固有存在。涡旋形态很可能印记了涡旋形成时冻结的信息，为相变早期存在的局部相位差提供了见解。
英文摘要
Observation of spontaneous symmetry breaking is crucial for understanding continuous second-order phase transitions from disordered to ordered states, which often leads to the formation of topological defects. In superconductors, such topological defects manifest as quantized vortices. However, the formation and observation of spontaneous vortices in a uniform superconductor are challenging because extremely rapid cooling (>108 K/s) is generally required for that purpose. Here we conducted scanning superconducting quantum interference device microscope (SSM) measurements on an MgB2-based proximity-induced superconductor, an intrinsically inhomogeneous system. In this system, individual superconducting domains will reach internal equilibrium independently during cooling and choose their own phase before the global phase coherence is established via the long-range proximity coupling. The SSM measurements demonstrate that vortices are nucleated spontaneously even at a relatively slow cooling rate (~0.2 K/s). We also find that the vortices with different polarities, sizes, and shapes appear stochastically under near-zero-field conditions. The geometry of the spontaneous vortices is more extended than that of the field-induced Abrikosov vortices. Magnetic field profile analysis based on the London model elucidates that penetration depths of the extended vortices are anomalously large, exceeding several micrometers. This unusual morphology of the spontaneous vortices most likely imprints the information that is frozen at the moment of vortex formation. Our findings not only provide insights into the local phase differences present in the early stage of the phase transition in this proximity-induced superconducting system, but they also shed insights into the structure, formation, and stabilization of topological defects in highly disordered and inhomogeneous superconducting systems.
Comments24 pages, 8 figures
