FULDE-FERRELL-LARKIN-OVCHINNIKOV STATE IN LAYERED SUPERCONDUCTORS

The phase diagram of a layered superconductor in a large parallel magn etic field is calculated. This includes a calculation of the lower cri tical field beyond which the superconductor is in the FFLO-state and p ossesses a spatially modulated order parameter and spin polarization. The order parameter, spin polarization, free-energy density, and phase boundaries of this unconventional superconducting phase are evaluated numerically in the complete B - T plane. The analysis suggests that t he transition at the lower critical field is of second order, and not of first order, as previously assumed. The order parameter of the FFLO -state merges continuously into the uniform superconducting state.