ISSN:
1573-7357
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract Using combined resistivity, susceptibility, critical field, and NMR measurements it was found that Al films with enhanced superconductivity can be divided into two separate categories depending on their residual resistivities ϱ0. Films with resistivities smaller than ⋍10 −3 Ω·cm are metallic (ϱ(300K)/ϱ 0 is larger than but very close to unity); the experimentally measured penetration depth, the upper critical field H⊥, and the penetration field Hp are in good agreement with theoretically calculated values using an experimental value of the mean free path1 eff. The density of states for such films as inferred from NMR measurements is very close to that of bulk. On the other hand, films with ϱ 0 larger than ⋍10 −3 Ω·cm have a semiconducting behavior (ϱ 300 K/ϱ 0 ≤1) and are grossly inhomogeneous. The experimental values of H⊥ no longer agree with the theoretical estimates using1 eff. In such films ϱ 0 is no longer a meaningful parameter that can be related to1 eff, for it is to a large extent a tunneling resistivity as shown by the fact that films not superconducting down to 0.95 K, when measured resistively, are superconducting at 1.2 K, as shown by a susceptibility measurement. These experiments seem to indicate that in a homogeneous film1 eff has a lower limit of approximately 1 Å.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00660071
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