Angular dependence of the upper critical field of superconductors

In this paper a theory of the upper critical magnetic field, Hc2, of anisotropic superconductors is discussed. This theory allows the calculation of the angular dependence of Hc2 in anisotropic systems with arbitrary impurity content. The model includes an electron-phonon-coupling anisotropy by use of a Fermi-surface-harmonics expansion. For simplicity, the model is restricted to the case of weak anisotropies. The key features of the model are discussed numerically using a simple separable model anisotropy