Renormalization-group calculations with k∥-dependent couplings in a ladder -: art. no. 045120

We calculate the phase diagram of a ladder system, with a Hubbard interaction and an interchain coupling t(perpendicular to). We use a renormalization-group method, in a one loop expansion, introducing an original method to include k(parallel to) dependence of couplings. We also classify the order parameters corresponding to ladder instabilities. We obtain different results, depending on whether we include k(parallel to) dependence or not. When we do so, we observe a region with large antiferromagnetic fluctuations, in the vicinity of small t(perpendicular to), followed by a superconducting region with a simultaneous divergence of the spin density waves channel. We also investigate the effect of a nonlocal backward interchain scattering: we observe, on one hand, the suppression of singlet superconductivity and of spin density waves, and, on the other hand, the increase of charge density waves and, for some values of t(perpendicular to), of triplet superconductivity. Our results eventually show that k(parallel to) is an influential variable in the renormalization-group flow, for this kind of system.