How the vortex lattice of a superconductor becomes disordered: a study by scanning tunneling spectroscopy

TL;DR

This paper uses scanning tunneling spectroscopy to visualize the stages of defect formation in a superconductor's vortex lattice during an order-disorder transition, revealing microscopic defect evolution and its relation to macroscopic properties.

Contribution

It provides real-space images of vortex lattice defect evolution during the transition, highlighting the change from dislocation pairs to clusters and the presence of a hexatic-like state.

Findings

Defect types evolve from dislocation pairs to clusters

A hexatic-like state appears before full disorder

The vortex transition correlates with the second peak effect in current density

Abstract

Order-disorder transitions take place in many physical systems, but observing them in detail in real materials is difficult. In two- or quasi-two-dimensional systems, the transition has been studied by computer simulations and experimentally in electron sheets, dusty plasmas, colloidal and other systems. Here I show the different stages of defect formation in the vortex lattice of a superconductor while it undergoes an order-disorder transition by presenting real-space images of the lattice from scanning tunneling spectroscopy. When the system evolves from the ordered to the disordered state, the predominant kind of defect changes from dislocation pairs to single dislocations, and finally to defect clusters forming grain boundaries. Correlation functions indicate a hexatic-like state preceding the disordered state. The transition in the microscopic vortex distribution is mirrored by the well-known spectacular second peak effect observed in the macroscopic current density of the superconductor.