Disorder can have remarkably disparate consequences in superconductors, driving superconductor-insulator transitions in ultrathin films by localizing electron pairs and boosting the supercurrent carrying capacity of thick films by localizing vortices (magnetic flux lines). Though the electronic 3D-to-2D crossover at material thicknesses $d \sim ξ$ (coherence length) is well studied, a similarly consequential magnetic crossover at $d \sim L_c$ (pinning length) that should drastically alter material properties remains largely underexamined. According to collective pinning theory, vortex segments of length $L_c$ bend to adjust to energy wells provided by point defects. Consequently, if $d$ truncates $L_c$, a change from elastic to rigid vortex dynamics should increase the rate of thermally activated vortex motion $S$. Here, we characterize the dependence of $S$ on sample thickness in Nb and cuprate films. The results for Nb are consistent with collective pinning theory, whereas creep in the cuprate is strongly influenced by sparse large precipitates. We leverage the sensitivity of $S$ to $d$ to determine the generally unknown scale $L_c$, establishing a new route for extracting pinning lengths in heterogeneously disordered materials.
Destruction of superconductivity in disordered materials : a dimensional crossover
通过改变样品厚度$d$，研究了不同Nb组分$x$的非晶Nb $_{x}$ Si $_{1-x}$二维薄膜中无序诱导的超导体-绝缘体转变.我们表明，临界厚度$d_c$，从绝缘的超导制度，随着减少$x$强烈增加，从而达到超过100欧姆的值。相应的相图中的$(d, x)$平面推断和相关的三维情况。二维的超导体到绝缘体的转变与三维的超导体到金属的转变良好连接。
