Anisotropy of the upper critical field in a heavy-fermion superconductor

We study the upper critical field for various possible order parameters of a heavy-fermion superconductor. We pay particular attention to the question of how the anisotropy of the upper critical field changes by effects of paramagnetism, impurity scattering, and Fermi-surface anisotropy in the presence of strong spin-orbit coupling. The paramagnetic limit can have a dramatic effect on the anisotropy in odd-parity superconductors, and provide important information on the symmetry of underlying order parameters. We also discuss the effect of impurity scattering.