Upper critical field of superconducting anisotropic polycrystals

M. Prohammer; E. Schachinger

doi:10.1103/PhysRevB.36.8353

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Upper critical field of superconducting anisotropic polycrystals

M. Prohammer, E. Schachinger

DOI 10.1103/PhysRevB.36.8353 · Physical Review B

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Abstract

We present a theory of the upper critical field for an anisotropic polycrystal. This theory is based on the well-known separable model for the electron-phonon anisotropy which is expanded to describe the Fermi-velocity anisotropy. It is assumed to be sufficient to describe these anisotropies by the mean-square parameters 〈a2〉 and 〈b2〉, respectively. Comparison with existing N-band models shows that our model only allows formation of Cooper pairs from quasiparticles which belong to the same Fermi-surface sheet. Predictions of this theory are discussed using a model system emphasizing the deviation of the upper critical field of the anisotropic system from an equivalent isotropic one. Finally, a procedure is suggested which should enable experimentalists to make a more detailed analysis of experimental data in terms of anisotropy effects.