Ginzburg-Landau和Kramer-Watts-Tobin模型下热涨落对均匀和非均匀超导环的影响
Influence of Thermal Fluctuations on Uniform and Nonuniform Superconducting Rings according to the Ginzburg--Landau and the Kramer--Watts-Tobin Models
摘要：
我们评估的影响，封闭的磁通量的超导环的热涨落，使用时间相关的金兹伯格-朗道（TDGL）或Kramer-瓦特-托宾（KWT）模型，而热涨落占通过朗之万条款。这种方法适用于以前的方法不适用的情况，如非均匀环，大宽径比的环和大相干长度与周长比的环。我们评估持续电流，位置和统计行为的磁通量诱导的旋涡和寿命的亚稳态磁通量态。非均匀性对持续电流的影响并不强烈地依赖于横截面轮廓的细节;它主要取决于它的第一谐波，但不仅在it. As的结果的非均匀性的持续电流的最大值转移到较小的通量和磁通量状态之间的通道保持非滞后下降到较低的温度比在均匀样品的情况下。我们的结果使用TDGL同意非常好，最近的测量超导环中的持续电流和测量的位置的涡流，介导的磁通量之间的状态，在一个不对称的磁盘与孔，他们也可以提供一个合理的解释，意想不到的短测量寿命的亚稳态。TDGL和KWT的比较表明，它们导致相同的结果的持续电流，而KWT导致更大的寿命比TDGL。
英文摘要：
We evaluate the influence of thermal fluctuations on superconducting rings that enclose a magnetic flux, using the time-dependent Ginzburg--Landau (TDGL) or the Kramer--Watts-Tobin (KWT) model, while thermal fluctuations are accounted for by means of Langevin terms. This method is applicable in situations where previous methods are not, such as nonuniform loops, rings with large width to radius ratio and loops with large coherence length to perimeter ratio. We evaluate persistent currents, position and statistical behavior of flux-induced vortices and lifetime of metastable fluxoid states. The influence of nonuniformity on the persistent current does not depend strongly on the details of the cross-section profile; it depends mainly on its first harmonic, but not only on it. As a consequence of nonuniformity the maximum of the persistent current shifts to smaller fluxes and the passage between fluxoid states remains non-hysteretic down to lower temperatures than in the case of a uniform sample. Our results using TDGL agree remarkably well with recent measurements of the persistent current in superconducting rings and with measurements of the position of a vortex that mediates between fluxoid states in an asymmetric disk with a hole; they could also provide a plausible explanation for unexpectedly short measured lifetimes of metastable states. Comparison between TDGL and KWT indicates that they lead to the same results for the persistent current, whereas KWT leads to larger lifetimes than TDGL.
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