Spin-liquid and magnetic phases in the anisotropic triangular lattice: the case of k-(ET)_2X

The two-dimensional Hubbard model on the anisotropic triangular lattice, with two different hopping amplitudes t and t('), is relevant to describe the low-energy physics of kappa-(ET)(2)X, a family of organic salts. The ground-state properties of this model are studied by using Monte Carlo techniques, on the basis of a recent definition of backflow correlations for strongly correlated lattice systems. The results show that there is no magnetic order for reasonably large values of the electron-electron interaction U and frustrating ratio t(')/t=0.85, suitable to describe the nonmagnetic compound with X=Cu-2(CN)(3). On the contrary, Neacuteel order takes place for weaker frustrations, i.e., t(')/t similar to 0.4-0.6, suitable for materials with X=Cu-2(SCN)(2), Cu[N(CN)(2)]Cl, or Cu[N(CN)(2)]Br.