STM Imaging of Flux Line Arrangements in the Peak Effect Regime

TL;DR

This study uses STM to observe vortex arrangements in 2H-NbSe2, revealing a disorder-driven transition at the peak effect where vortex pinning dominates elastic forces.

Contribution

First direct imaging of vortex behavior across the peak effect regime, linking disorder and pinning to vortex dynamics in superconductors.

Findings

Sharp transition from collective motion to individual vortex fluctuations

Peak effect coincides with the onset of positional fluctuations

Disorder-driven transition where pinning energy surpasses elastic energy

Abstract

We present the results of a study of vortex arrangements in the peak-effect regime of 2H-NbSe_2 by scanning tunneling microscopy. By slowly increasing the temperature in a constant magnetic field, we observed a sharp transition from collective vortex motion to positional fluctuations of individual vortices at the temperature which coincides with the onset of the peak effect in ac-susceptibility. We conclude that the peak effect is a disorder driven transition, with the pinning energy winning from the elastic energy.