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The effect of epitaxy on the upper critical fields of evaporated niobium films

Published online by Cambridge University Press:  31 January 2011

Gin-ichiro Oya ,
Tetsuro Komukai  and
Yasuji Sawada
Gin-ichiro Oya
Affiliation:
Research Institute of Electrical Communication, Tohoku University, Sendai 980, Japan
Tetsuro Komukai
Affiliation:
Research Institute of Electrical Communication, Tohoku University, Sendai 980, Japan
Yasuji Sawada
Affiliation:
Research Institute of Electrical Communication, Tohoku University, Sendai 980, Japan
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Abstract

Two upper critical fields normal (Bc2⊥) and parallel (Bc2∥) to the surfaces of both single-crystal and polycrystalline Nb films are studied at 4.2 K in relation to the purity and morphology of the films, in order to make properties of the single-crystal films clear. High-quality single-crystal Nb films (with transition temperature Tc of ∼9.3 K and normal resistivity ρn of ∼0.2 μΩ · cm) are found to have magnetic properties characterized by Bc2⊥ of 0.31 T as low as Bc2 (bulk upper critical field) of bulk Nb, and Bc2∥/Bc2⊥ of ∼1.85 as high as Bc3/Bc2 (where Bc3 is the surface nucleation critical field) of pure Nb. These properties depend strongly on high purity and surface smoothness of the films, which is naturally accompanied by superconductivity. Polycrystalline Nb films have higher Bc2⊥ and lower Bc2∥/Bc2⊥, which result from a decrease in purity of the films and a presence of normal-conducting niobium-suboxide layers at the surfaces of the films, and thereby a decrease of the surface effect in the films.

Type
Articles
Information
Journal of Materials Research , Volume 4 , Issue 2 , April 1989 , pp. 283 - 287
Copyright
Copyright © Materials Research Society 1989

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References

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