Competition between SDW and SC states in two-Hubbard chains

Two coupled chains of Hubbard model with spin anisotropic backward scattering have been studied by applying the renormalization group method to the bosonized Hamiltonian. From two kinds of fixed points for transverse spin fluctuations, which exist in the presence of anisotropic interactions, it has been shown that the dominant state moves from a singlet superconducting (SC) state with interchain pairing into a longitudinal spin density wave (SDW) state with intrachain pairing when the repulsive interaction increases. Phase diagram at finite temperatures is also obtained.