Crossover from Vortex States to the Fulde-Ferrell- Larkin-Ovchinnikov State in Two-Dimensional s- and d-Wave Superconductors

Abstract

The effects of a tilted magnetic field on two-dimensional type-II superconductors of s- and d-wave pairing are studied. This includes a study of the crossover from vortex states to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state when the direction of the magnetic field is changed from perpendicular to the conducting plane to a parallel orientation. The FFLO state is obtained in the limit of a parallel magnetic field, and vortex phases with a large quantum number n>0 (a higher Landau level) appear for tilted magnetic fields. At fixed tilt angle, the critical field exhibits a characteristic gtemperature dependence due to the change of the discrete quantum number. The relevance of the results for the observation and the identification of the FFLO state in the organic and T_c superconductors is discussed.