A study of superconductivity in single crystals and thin films using muon-spin rotation and neutron scattering

Abstract

The archetypal high temperature superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] has been extensively investigated. However, until now, little has been known about the behaviour of the magnetic vortices inside the Vortex Glass and liquid state. µSR measurements have shown a negative skewness for the field probability distributions in these regimes. Such a negative skewness has only recently been explained as being a direct consequence of three-body correlations between vortices in a similar layered superconductor. With a new understanding and knowledge of the physics of these systems, it is instructive to re-visit the superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] to explain the evolution of these three-body correlations occurring here. Comparing this with the ion-irradiated superconductors (of the same Bi₂Sr₂CaCu₂O[subscript[8+δ]] material), allows one to observe how three-body correlations between vortices evolve differently to that in the pristine material. Moreover, in the region of the macroscopic irreversibility line, entropically driven disorder exists below the matching field B[subscript[ϕ]] , whilst there is the appearance of relatively straight vortex lines at fields above B[subscript[ϕ]] . Such phenomena suggest a significant di fference in the evolution of three-body correlations compared with the unirradiated material. There has been much work conducted on the interplay between superconductivity and magnetism in materials of reduced dimensions. Work presented here on the ferromagnet/superconductor trilayer system (Permalloy/Nb/Permalloy) has shown a novel magnetic profile at the interface between the ferromagnetic and superconducting boundary, where, contrary to what is expected, the magnetism appears to be significantly suppressed at the interface before increasing towards the centre of the Nb layer.