AI 中文总结
本研究通过调控块状NbTi的界面热边界电导，观测到阈值场温度依赖的非单调变化，证实了热磁雪崩过渡 regime 的 onset 存在，为超导体热磁不稳定性的调控提供了实验依据。
AI 中文摘要
第二类超导体中的热磁雪崩以两种性质不同的 regime 发生：薄膜中为电磁控制 regime，块状样品中为热限制 regime，二者由阈值场 $H_\text{th}(T)$ 的温度导数符号区分。两种 regime 被临界热边界电导 $h_c$ 分隔，且在界面电导 $h$ 趋近 $h_c$ 的过渡区域，理论预测存在非单调的 $H_\text{th}(T)$。我们通过在纯正十九烷基线之上填充银的界面层提升界面耦合，在块状NbTi圆盘中逼近该过渡区域。纯界面给出单调递减的 $H_\text{th}(T)$，而填充银的界面产生块状超导体中此前未观测到的非单调依赖关系：存在一个正斜率的温度区间，$dH_\text{th}/dT > 0$，在 $T^* \approx 6.1$--$6.4$ K 处达到最大值。该效应在两种独立的银填充成分中均得到重现；在第三种负载最高的样品中，低温下降完全消失，$H_\text{th}(T)$ 保持平坦直至相同的 $T^*$，这是更强耦合的预期演化。最大值的位置由NbTi的本征性质决定，与银含量无关。正斜率区间的温度与雪崩形态从窄通道状指状转变为宽前沿的温度变化重合。$dH_\text{th}/dT$ 符号的反转是过渡 regime onset 的直接实验信号，该 regime 中不稳定性期间的散热具有动态相关性。
英文摘要
Thermomagnetic avalanches in type-II superconductors occur in two qualitatively different regimes, electromagnetically controlled in thin films and thermally limited in bulk samples, distinguished by the sign of the temperature derivative of the threshold field $H_\text{th}(T)$. The two regimes are separated by a critical thermal boundary conductance $h_c$, and a non-monotonic $H_\text{th}(T)$ has been predicted in the transitional region where the interface conductance $h$ approaches $h_c$. We approach this region in a bulk NbTi disk by raising the interface coupling above the pure-nonadecane baseline with a silver-filled interface layer. Whereas the pure interface gives a monotonically decreasing $H_\text{th}(T)$, the silver-filled interface produces a non-monotonic dependence not previously realized in a bulk superconductor: a temperature interval of positive slope, $dH_\text{th}/dT > 0$, terminating in a maximum at $T^* \approx 6.1$--$6.4$~K. The effect is reproduced for two independent silver-filled compositions; in a third, with the highest loading, the low-temperature decrease is absent altogether and $H_\text{th}(T)$ is flat up to the same $T^*$, the evolution expected for stronger coupling. The position of the maximum is set by the intrinsic properties of NbTi, independent of the silver content. The onset of the positive-slope interval coincides in temperature with a change of the avalanche morphology from narrow channeled fingers to broad fronts. The reversal of the sign of $dH_\text{th}/dT$ is a direct experimental signature of the onset of the transitional regime, in which heat removal during the instability becomes dynamically relevant.
Comments10 pages, 3 figures
