Two step disordering of the vortex lattice across the peak effect in a weakly pinned Type II superconductor, Co0.0075NbSe2

TL;DR

This study reveals a two-step disordering process of the vortex lattice in a weakly pinned Type II superconductor, involving a transition from Bragg glass to orientational glass and then to amorphous vortex glass, with metastable states observed.

Contribution

It provides direct experimental evidence of a two-step disordering mechanism in the vortex lattice of Co0.0075NbSe2 using scanning tunnelling spectroscopy.

Findings

Disordering occurs in two steps across the peak effect.

Transition from Bragg glass to orientational glass involves dislocation proliferation.

Further transition to amorphous vortex glass involves disclination dissociation.

Abstract

The vortex lattice in a Type II superconductor provides a versatile model system to investigate the order-disorder transition in a periodic medium in the presence of random pinning. Here, using scanning tunnelling spectroscopy in a weakly pinned Co0.0075NbSe2 single crystal, we show that at low temperatures, the vortex lattice in a 3-dimensional superconductor disorders in two steps across the peak effect. At the onset of the peak effect, the equilibrium Bragg glass transforms into an orientational glass through the proliferation of dislocations. At a higher field, the dislocations dissociate into isolated disclination giving rise to an amorphous vortex glass. We also show the existence of a variety of additional non-equilibrium metastable states, which can be accessed through different thermomagnetic cycling.