Upper critical field of inhomogeneous superconductors

Yuan, Bojiong (1994) Upper critical field of inhomogeneous superconductors. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (22MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The thesis consists of two distinct but closely related parts. In the first part we present an analysis of the angular dependence of the upper critical field of a type II superconducting film, using the de Gennes-Werthamer formalism. The results are presented for a range of thicknesses, which includes the special case of the semi-infinite geometry, and for all orientations 0 < θ < π/2. It is shown that careful consideration is required to recover the limiting parallel field case (θ → 0) from the finite θ calculation. A comparison with earlier work in this area is given and it is shown that more detailed and systematic experimental studies are required in order to resolve the differences between experiment and theory. In the second part, the temperature dependence of the parallel upper critical field for a layered superconductor is investigated within the framework of de Gennes-Werthamer theory. The resultant upper critical field curves are shown to be strongly dependent upon the presence of the free surface and the character of the initial layer deposited on an insulated substrate. A direct comparison of the calculated upper critical field curves with the experimental results on Nb/NbZr layered structures is given. The results are in good agreement provided the pair-breaking effect of the spin paramagnetism is included.

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