Accelerated vortex dynamics across the magnetic 3D-to-2D crossover in disordered superconductors

TL;DR

This study investigates how the magnetic vortex dynamics in disordered superconductors change across the electronic 3D-to-2D crossover, revealing a new method to measure pinning lengths and understanding vortex behavior.

Contribution

It introduces a novel approach to determine the pinning length scale $L_c$ by analyzing vortex creep rates across the thickness transition in disordered superconductors.

Findings

Vortex creep rate $S$ depends on sample thickness $d$ in Nb and cuprate films.

In Nb, results align with collective pinning theory predictions.

In cuprates, vortex creep is affected by large precipitates, deviating from theory.

Abstract

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 $d \sim \xi$ (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.