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H c ( θ ) and Tinkham's Formula for High-Field Superconductors

1973; American Physical Society; Volume: 7; Issue: 1 Linguagem: Inglês

10.1103/physrevb.7.554

0556-2805

Koya Aoi, R. Meservey, P. M. Tedrow,

Superconductivity in MgB2 and Alloys

We report measurements of the angular dependence of the upper critical field ${H}_{c}(\ensuremath{\theta})$ of two-dimensional high-field superconductors (thin Al films). The results are found to be in good agreement with the theory of Fulde and Maki and of Werthamer, Helfand, and Hohenberg. It is shown that, unless the sample is very dirty and the temperature is low ($T\ensuremath{\ll}{T}_{c}$). Tinkham's formula, which was originally derived without including Pauli paramagnetism, describes well the angular dependence even in the case where ${H}_{c}$ is limited by Pauli paramagnetism. We also show that in a thin film, in constrast to a bulk material, Pauli paramagnetism can limit ${H}_{c\ensuremath{\parallel}}$, even at temperatures close to ${T}_{c}$.