弓弦效应作为薄超导体中磁通不稳定性的触发因素
Bowstring effect as a trigger for flux instabilities in thin superconductors
AI总结：
本文提出磁涡旋穿入扁平超导体时的“弓弦效应”可释放热量并触发磁通雪崩，推导了圆盘和条形样品的阈值场及热效应，并用各向异性解释相关实验现象。
摘要：
在磁涡旋穿入矩形截面扁平超导样品的初始阶段，它们类似于拉过拐角的弓弦。当外磁场 $H_e$ 达到阈值水平 $H_{th}$ 时，弓弦被“释放”，并瞬间收缩长度，同时产生大量热量。这种热量可作为磁通不稳定性（雪崩）成核的触发因素。在 $H_e \approx \sqrt{2}H_{th}$ 时，通常的涡旋穿入从平直边缘开始，弓弦机制不再有效。我们描述了弓弦状涡旋的几何结构，求出了圆盘形和条形超导体的 $H_{th}$ 作为其厚宽比函数的表达式，并确定了与弓弦释放相关的热效应。我们的结果使人们能够以一种新的方式处理关于扁平超导样品中磁通不稳定性和雪崩式穿入的大量实验数据。超导穿透深度的适度各向异性（$λ_c > λ_{ab}$）会减弱甚至完全消除弓弦效应。这解释了为何外延 $\mathrm{YBa}_{2}\mathrm{Cu}_{3}\mathrm{O}_{7-δ}$ 薄膜在所有温度下以及 $\mathrm{MgB_{2}}$ 在 10 K 以上都不存在自发不稳定性。
英文摘要：
Magnetic vortices resemble bowstrings stretched across a corner at the initial stage of their penetration into a flat superconducting sample of a rectangular cross-section. As the external magnetic field $H_e$ reaches the threshold level $H_{th}$, a bowstring is "released" and instantaneously contracted in length with a substantial heat generation. This heat can serve as a trigger for nucleation of a flux instability (avalanche). At $H_e \approx \sqrt{2}H_{th}$ a usual vortex penetration starts at flat edges, and the bowstring mechanism is no longer effective. We describe the geometry of bowstring-like vortices, find $H_{th}$ for disk and strip shaped superconductors as a function of their thickness to width ratio, and determine the heat effect related to a bowstring release. Our results enable a novel treatment of numerous experimental data on flux instabilities and avalanche type penetration in flat superconducting samples. A moderate anisotropy of a superconducting penetration depth ($λ_c > λ_{ab}$) diminishes or even completely removes the bowstring effect. This explains the absence of spontaneous instabilities in epitaxial $\mathrm{YBa}_{2}\mathrm{Cu}_{3}\mathrm{O}_{7-δ}$ films at all temperatures and in $\mathrm{MgB_{2}}$ above 10 K.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
