Direct Evidence for Edge-Contaminated Vortex Phase in a Nb Single   Crystal using Neutron Diffraction
  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. 
Helen A. Hanson, Xi Wang, Ivo K. Dimitrov, Jing Shi, Xinsheng Sean   Ling, Charles F. Majkrzak, Brian B. Maranville, Mark La...
cond-mat.supr-con cond-mat.mtrl-sci