Limited role of vortices in transport in highly disordered superconductors near $B_{c2}$

TL;DR

This study reveals that in amorphous indium oxide superconducting films near the upper critical field, vortex motion plays a minimal role in electrical resistance, challenging traditional views on vortex-driven transport in disordered superconductors.

Contribution

The paper demonstrates that vortex-related effects are negligible in transport near $B_{c2}$ in highly disordered amorphous indium oxide films, showing isotropic resistance behavior regardless of magnetic field orientation.

Findings

Resistance near $B_{c2}$ is nearly isotropic for different magnetic field orientations.

Transport properties are insensitive to magnetic field orientation after rescaling.

Isotropic behavior persists into the insulating phase beyond the superconductor-insulator transition.

Abstract

At finite temperatures and magnetic fields, type-II superconductors in the mixed state have a non-zero resistance that is overwhelmingly associated with vortex motion. In this work we study amorphous indium oxide films, which are thicker than the superconducting coherence length, and show that near $B_{c2}$ their resistance in the presence of perpendicular and in-plane magnetic fields becomes almost isotropic. Up to a linear rescaling of the magnetic fields both the equilibrium resistance as well as the non-equilibrium current-voltage characteristics are insensitive to magnetic field orientation suggesting that, for our superconductors, there is no fundamental difference in transport between perpendicular and in-plane magnetic fields. Additionally we show that this near-isotropic behavior extends to the insulating phase of amorphous indium oxide films of larger disorder strength that undergo a magnetic field driven superconductor-insulator transition. This near-isotropic behavior raises questions regarding the role of vortices in transport and the origin of resistance in thin-film superconductors.