Superconducting transition of a two-dimensional Josephson junction array in weak magnetic fields

TL;DR

This study investigates the superconducting transition in a 2D Josephson junction array under weak magnetic fields, revealing unexpected phase boundary behavior and challenging existing vortex transition theories.

Contribution

It provides experimental evidence that contradicts theoretical predictions about vortex melting and depinning transitions in weak magnetic fields.

Findings

Superconducting-resistive phase boundary disagrees with models.

Vortex depinning transition was not observed.

Disorder-induced pinning affects vortex phase transitions.

Abstract

The superconducting transition of a two-dimensional (2D) Josephson junction array exposed to weak magnetic fields has been studied experimentally. Resistance measurements reveal a superconducting-resistive phase boundary in serious disagreement with the theoretical and numerical expectations. Critical scaling analyses of the $IV$ characteristics indicate contrary to the expectations that the superconducting-to-resistive transition in weak magnetic fields is associated with a melting transition of magnetic-field-induced vortices directly from a pinned-solid phase to a liquid phase. The expected depinning transition of vortices from a pinned-solid phase to an intermediate floating-solid phase was not observed. We discuss effects of the disorder-induced random pinning potential on phase transitions of vortices in a 2D Josephson junction array.