Vortex trapping and expulsion in thin-film type-II superconducting strips

微观结构对超导射频腔磁通排出作用的研究

Role of microstructure on flux expulsion of superconducting radio frequency cavities

本文研究了铌微观结构对超导射频腔磁通排出的影响，发现传统退火铌板经800°C热处理后产生双峰微观结构导致磁通捕获，而采用冷加工铌板制造1.3 GHz单腔并结合热处理可显著改善磁通排出性能，证实了微观结构对降低超导腔射频损耗的关键作用。

Flux expulsion in niobium superconducting radio-frequency cavities of different purity and essential contributions to the flux sensitivity

Magnetic flux trapped during the cooldown of superconducting radio-frequency cavities through the transition temperature due to incomplete Meissner state is known to be a significant source of radio-frequency losses. The sensitivity of flux trapping depends on the distribution and the type of defects and impurities which pin vortices, as well as the cooldown dynamics when the cavity transitions from a normal to superconducting state. Here we present the results of measurements of the flux trapping sensitivity on 1.3 GHz elliptical cavities made from large-grain niobium with different purity fo…

窄均匀超导条带在小磁场冷却后冻结磁通的理论

Theory of frozen flux in a narrow uniform superconducting strip after cooling in a small magnetic field

通过分析窄超导条带在垂直小磁场中冷却时涡旋的动力学平衡，推导了冻结温度与冻结涡旋密度的定量结果，揭示了磁场和冷却速率对冻结磁通的强依赖性。

Mesoscopic cross-film cryotrons: Vortex trapping and dc-Josephson-like oscillations of the critical current

We investigate theoretically and experimentally the transport properties of a plain Al superconducting strip in the presence of a single straight current-carrying wire, oriented perpendicular to the superconducting strip. It is well known that the critical current of the superconducting strip, Ic, in such cryotron--like system can be tuned by changing the current in the control wire, Iw. We demonstrated that the discrete change in the number of the pinned vortices/antivortices inside the narrow and long strip nearby the current-carrying wire results in a peculiar oscillatory dependence of Ic o…

通过工程化非均匀Pearl长度调控窄薄膜超导体的临界场、临界电流与二极管效应

Tuning critical field, critical current, and diode effect of narrow thin-film superconductors through engineering inhomogeneous Pearl length

本文通过理论计算证明，在窄薄膜超导体中工程化设计非均匀Pearl长度分布，可在不减小带宽的前提下提高临界场和临界电流，并实现超导二极管效应。

Dependence of the residual surface resistance of superconducting RF cavities on the cooling dynamics around $T_\mathrm{c}$

We report a strong effect of the cooling dynamics through $T_\mathrm{c}$ on the amount of trapped external magnetic flux in superconducting niobium cavities. The effect is similar for fine grain and single crystal niobium and all surface treatments including electropolishing with and without 120$^\circ$C baking and nitrogen doping. Direct magnetic field measurements on the cavity walls show that the effect stems from changes in the flux trapping efficiency: slow cooling leads to almost complete flux trapping and higher residual resistance while fast cooling leads to the much more efficient flu…

Vortex Trapping in Hybrid Magnetometers

Hybrid magnetometers based on a normal conducting sensor and a superconducting flux concentrator have been investigated. When this sensor is operated in an unshielded environment flux vortices can be trapped in the superconducting body when the sensor is cooled. Thermal hopping of the trapped vortices gives rise to 1/f noise. The mechanism for vortex trapping has been investigated. A new model for the critical field for vortex trapping and vortex densities has been derived. Experimental verification on YBa2Cu3O7-delta (YBCO) strips with a Scanning SQUID Microscope shows very good agreement bet…

利用沟槽抑制超导电子中的磁通量陷阱

Mitigation of Magnetic Flux Trapping in Superconducting Electronics Using Moats

本研究系统地探讨了在超导铌薄膜中使用沟槽阵列抑制磁通量陷阱的有效性，通过测量涡流排斥场估算不同几何形状下的磁通饱和数和磁通陷阱温度，发现高宽比的矩形'槽'状沟槽在最小面积成本下提供最强的抑制效果，但沟槽单独使用无法完全消除非理想薄膜中的磁通量陷阱。

Similarity between Ni and Zn impurity effects on the superconductivity and Cu-spin correlation in La2-xSrxCu1-yNiyO4 high-Tc cuprates: A comparison based on the hole trapping by Ni

Ni-substitution effects on the superconductivity and Cu-spin correlation have been investigated in La2-xSrxCu1-yNiyO4 from the electrical resistivity and muon spin relaxation measurements, taking into account the hole trapping by Ni recently suggested. It has been found that the Ni-substitution suppresses the superconductivity, induces the localization of holes and develops the Cu-spin correlation to the same degree as the Zn substitution. These suggest that Ni with a trapped hole tends to give rise to potential scattering of holes in the CuO2 plane to the same degree as Zn, being discussed in…

Design of magnetic traps for neutral atoms with vortices in type-II superconducting micro-structures

We design magnetic traps for atoms based on the average magnetic field of vortices induced in a type-II superconducting thin film. This magnetic field is the critical ingredient of the demonstrated vortex-based atom traps, which operate without transport current. We use Bean's critical-state method to model the vortex field through mesoscopic supercurrents induced in the thin strip. The resulting inhomogeneous magnetic fields are studied in detail and compared to those generated by multiple normally-conducting wires with transport currents. Various vortex patterns can be obtained by programmin…

History effects and pinning regimes in solid vortex matter

We propose a phenomenological model that accounts for the history effects observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys. Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the model is the assumption that the penetrating ac magnetic field modifies the vortex lattice mobility, trapping different robust dynamical states in different regions of the sample. We discuss in detail on the response of the superconductor to an ac magnetic field when the vortex lattice mobility is not uniform inside the sample. We begin with an analytical descripti…