We report the first direct observation of a disordered vortex matter phase existing near the edge of a bulk type-II superconductor Nb using a novel position-sensitive neutron diffraction technique. This "edge-contaminated" vortex state was implicated in previous studies using transport techniques and was postulated to have played a significant role in the behavior of vortex dynamics in a wide range of type-II superconductors. It is found that upon thermal annealing, the vortex matter in the bulk undergoes re-ordering, suggesting that the edge-contaminated bulk vortex state is metastable. The edge vortex state remains disordered after repeated thermal annealing, indicating spatial coexistence of a vortex glass with a Bragg glass. This observation resolves many outstanding issues concerning the peak effect in type-II superconductors.
@article{arxiv.1103.1273,
title = {Direct Evidence for Edge-Contaminated Vortex Phase in a Nb Single Crystal using Neutron Diffraction},
author = {Helen A. Hanson and Xi Wang and Ivo K. Dimitrov and Jing Shi and Xinsheng Sean Ling and Charles F. Majkrzak and Brian B. Maranville and Mark Laver and Uwe Keiderling and Margarita Russina},
journal= {arXiv preprint arXiv:1103.1273},
year = {2011}
}