Anisotropy of the upper critical field in exotic superconductors
Gor'kov L. P.
While the superconducting order parameter is characterized by a multidimensional representation of the rotation group (a state of the type 3He-A ), the upper critical field near Tc is anisotropic even in a crystal with a high degree of symmetry. This circumstance can be used to describe the nature of the observed superconductivity. The degeneracy can in principle be lifted by elastic stress.