The critical magnetic fields of heavy fermions superconductors

Abstract

The effects on the upper critical and lower critical fields of a system with two almost degenerate order parameters were considered. Within the first order perturbations, we write the two order parameters as linear combinations of the states |0> and |2>. The upper critical field is close to T_c = T₅ and occurs below a certain temperature T’. It can easily be seen that sharp change of HC₂ between the two solutions exists in all orders of perturbation because there is no finite matrix element between the two states (ƞ, ƞ₃) = (|0>, 0) and (ƞ, ƞ₃) = (0, |0>) in any higher order of perturbation in the coupling term. This is different if the Magnetic field is pointing along some arbitrary direction.