# Universal behavior of the IMS domain formation in superconducting niobium

## TL;DR

This study reveals a universal temperature-dependent behavior of vortex domain formation in the intermediate mixed state of superconducting niobium, independent of magnetic field and affected by vortex interactions and pinning.

## Contribution

It demonstrates the universal temperature dependence of vortex spacing in niobium's IMS, linking it to the London penetration depth and showing pinning breakdown at vortex attraction onset.

## Key findings

- Vortex lattice decomposes into dense domains with temperature-dependent spacing.
- Vortex spacing correlates with the London penetration depth.
- Pinning effects diminish at the vortex attraction transition.

## Abstract

In the intermediate mixed state (IMS) of type-II/1 superconductors, vortex lattice (VL) and Meissner state domains coexist due to a partially attractive vortex interaction. Using a neutron-based multiscale approach combined with magnetization measurements, we study the continuous decomposition of a homogeneous VL into increasingly dense domains in the IMS in bulk niobium samples of varying purity. We find a universal temperature dependence of the vortex spacing, closely related to the London penetration depth and independent of the external magnetic field. The rearrangement of vortices occurs even in the presence of a flux freezing transition, i.e. pronounced pinning, indicating a breakdown of pinning at the onset of the vortex attraction.