Pairing Competition in a Quasi-One-Dimensional Model of Organic Superconductors (TMTSF)₂X in Magnetic Field

抄録

We microscopically study the effect of the magnetic field (Zeeman splitting) on the superconducting state in a model for quasi-one-dimensional organic superconductors (TMTSF)₂X. We investigate the competition between spin singlet and spin triplet pairings and the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state by random phase approximation. While we studied the competition by comparison with the eigenvalue of the gap equation at a fixed temperature in our previous study [Phys. Rev. Lett. 102 (2009) 016403], here we obtain both the T_c for each pairing state and a phase diagram in the T (temperature)–h_z (field)–V_y (strength of the charge fluctuation) space. The phase diagram shows that consecutive transitions from singlet pairing to the FFLO state and further to S_z=1 triplet pairing can occur upon increasing the magnetic field when 2k_F charge fluctuations coexist with 2k_F spin fluctuations. In the FFLO state, the singlet d-wave and S_z=0 triplet f-wave components are strongly mixed especially when the charge fluctuations are strong.