Spontaneous vortex state and ferromagnetic behavior of type-II p-wave superconductors

The mixed phase in type-II superconductors with equal spin p-wave pairing is considered using the Ginzburg-Landau approach. Due to direct spin coupling of the condensate to magnetic field the mixed state acquires ferromagnetic properties. For sufficiently large Zeeman coupling a spontaneous vortex phase appears at H=0 and exists and for an arbitrarily large magnetic field. The Meissner phase therefore completely disappears. Vortices become thinner when H grows. There exists a value of Zeeman coupling above which, in the presence of external magnetic field, a mixed phase might occur even for temperatures above T_c. The structure of the vortex core is markedly different from the usual one.