Spin-gapped phases in the frustrated Hubbard chain with transverse spin anisotropy

At weak coupling, we investigate the frustrated Hubbard chain including nearest-neighbor and next-nearest-neighbor antiferromagnetic exchange with easy-plane anisotropy J1xy and J2xy. At half filling, we obtain three different phases in the J1xy-J2xy plane: a transverse spin density wave phase, a bond order wave phase and a Luther-Emery metallic phase characterized by the coexistence of singlet superconductivity and charge density wave correlations. The frustrating exchange J2xy accounts for the spin-gapped phases.