# Unveiling the vortex glass phase in the surface and volume of a type-II superconductor

## TL;DR

This study investigates the microscopic structure of the vortex glass phase in a type-II superconductor, revealing it has large crystallites with algebraic positional order and short-range orientational order, bridging surface and bulk observations.

## Contribution

It provides the first comprehensive structural characterization of the vortex glass phase using combined surface and bulk imaging techniques.

## Key findings

- Vortex glass exhibits large crystallites with algebraic positional correlations.
- Short-range orientational order is present in the vortex glass phase.
- No significant change in correlation length along vortex lines across the transition.

## Abstract

Order-disorder transitions between glassy phases are quite common in nature and yet a comprehensive survey of the microscopic structural changes remains elusive since the scale of the constituents is tiny and in most cases few of them take part in the transformation. Vortex matter in type-II superconductors is a model system where some of the experimental challenges inherent to this general question can be tackled by adequately choosing the host superconducting sample. For instance, Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8 + \delta}$ is a type-II superconductor with weak point disorder that presents a transition between two glassy phases on increasing the constituents' (vortices) density. At low vortex densities, the impact of disorder produces the nucleation of a glassy yet quasi-crystalline phase, the Bragg glass. For high vortex densities the stable phase, coined as $\textit{vortex glass}$, was proposed to be disordered, but its structural properties have remained elusive up to now. Here we answer this question by combining surface and bulk vortex imaging techniques, and show that the vortex glass is neither a messy nor a hexatic phase: in the plane of vortices it presents large crystallites with positional correlations growing algebraically and short-ranged orientational order. However, no dramatic change in the correlation length along the direction of vortices is observed on traversing the order-disorder transformation.