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

Superconductors;Vortex-motion;Crystals--Magnetic properties;Thin films--Magnetic properties

Heron, David Owen Goudie ; Lee, Stephen ; Lee, Stephen

University:University of St Andrews

Department:Physics & Astronomy (School of)

关键词: Superconductors;    Vortex-motion;    Crystals--Magnetic properties;    Thin films--Magnetic properties;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/742/David%20O.G.%20Heron%20PhD%20thesis.PDF?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

The archetypal high temperature superconductor Bi₂Sr₂CaCu₂O[subscript[8+δ]] has been extensively investigated. However, until now, little has been known about the behaviour of themagnetic vortices inside the Vortex Glass and liquid state. µSR measurements have showna negative skewness for the field probability distributions in these regimes. Such a negativeskewness has only recently been explained as being a direct consequence of three-body correlations between vortices in a similar layered superconductor. With a new understandingand 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 irreversibilityline, 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 asignificant di fference in the evolution of three-body correlations compared with the unirradiated material.There has been much work conducted on the interplay between superconductivityand magnetism in materials of reduced dimensions. Work presented here on the ferromagnet/superconductor trilayer system (Permalloy/Nb/Permalloy) has shown a novel magneticprofile at the interface between the ferromagnetic and superconducting boundary, where,contrary to what is expected, the magnetism appears to be significantly suppressed at theinterface before increasing towards the centre of the Nb layer.