Superconducting radio frequency (SRF) cavities, which are critical components in many particle accelerators, need to be operated in the Meissner state to avoid strong dissipation from magnetic vortices. For a defect-free superconductor, the maximum attainable magnetic field for operation is set by the superheating field, Bsh , which directly depends on the surface current. In heterostructures composed of different superconductors, the current in each layer depends not only on the properties of the individual material, but also on the electromagnetic response of the adjacent layers through boundary conditions at the interfaces. Three prototypical bilayers [ Nb1−xTixN (50nm)/Nb , Nb1−xTixN (80nm)/Nb , and, Nb1−xTixN (160nm)/Nb ] are investigated here by depth-resolved measurements of their Meissner screening profiles using low energy muon spin rotation (LE-µSR). From fits to a model based on London theory (with appropriate boundary and continuity conditions), a magnetic penetration depth for the thin Nb1−xTixN layers of λNb1−xTixN=182.5(31)nm is found, in good agreement with literature values for the bulk alloy. Using the measured λNb1−xTixN , the maximum vortex-free field, Bmax , of the superconductor-superconductor (SS) bilayer structure was estimated to be 610(40)mT . The strong suppression of the surface current in the Nb1−xTixN layer suggests an optimal thickness of ∼1.4λNb1−xTixN=261(14)nm.

中文翻译：

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超导-超导双层中电流抑制的证据

超导射频（SRF）腔是许多粒子加速器中的关键部件，需要在迈斯纳状态下运行，以避免磁涡流的强烈耗散。对于无缺陷超导体，操作时可达到的最大磁场由过热场设定， 乙sH ，这直接取决于表面电流。在由不同超导体组成的异质结构中，每层中的电流不仅取决于单个材料的特性，还取决于相邻层通过界面处边界条件的电磁响应。三个典型的双层[ 氮乙1-X时间我X氮 （50n米）/氮乙 , 氮乙1-X时间我X氮 （80n米）/氮乙 ， 和， 氮乙1-X时间我X氮 （160n米）/氮乙 ]在这里通过使用低能μ子自旋旋转（LE-µSR）。从拟合到基于伦敦理论（具有适当的边界和连续性条件）的模型，薄层的磁穿透深度 氮乙1-X时间我X氮 层数 λ氮乙1-X时间我X氮=182.5（31）n米 发现与大块合金的文献值非常一致。使用测量的 λ氮乙1-X时间我X氮 ，最大无涡场， 乙米AX ，超导-超导（SS）双层结构的估计为 610（40）米时间 。对表面电流的强烈抑制 氮乙1-X时间我X氮 层建议最佳厚度为 ～1.4λ氮乙1-X时间我X氮=261（14）n米。