Magnetic field effect on the pairing competition in quasi-one-dimensional organic superconductors (TMTSF)2X

We microscopically study the effect of the magnetic field (Zeeman splitting) on the superconducting state in a model for quasi-one-dimensional organic conductors (TMTSF)2X. Using random phase approximation, we investigate the competition between spin singlet, spin triplet pairings and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We obtain a phase diagram in the T (temperature)-hz (field) space. We show that consecutive transitions from singlet pairing to FFLO and further to Sz=1 triplet pairing can take place upon increasing the magnetic field when 2kF charge fluctuations coexist with 2kF spin fluctuations.