Symmetrized mean-field description of magnetic instabilities in kappa-(BEDT-TTF)(2)Cu[N(CN)](2)Y salts - art. no. 054509

We present a convenient mean-field method, and apply it to study the metall ic/antiferromagnetic interface of kappa-(BEDT-TTF)(2)Cu[N(CN)](2)Y organic superconductors (BEDT-TTF is bis-ethylendithio-tetrathiafulvalene, Y = Cl,B r). The method, which fully exploits the crystal symmetry, allows one to ob tain the mean-field solution of the two-dimensional Hubbard model for very large lattices (typically 6 x 10(5) sites), yielding a reliable description of the phase boundary in a wide region of the parameter space. The metal/a ntiferromagnet transition appears to be second order, except for a narrow r egion of the parameter space, where the transition is very sharp and possib ly first order. The coexistence of metallic and antiferromagnetic propertie s is only observed for the transient state in the case of smooth second ord er transitions. The relevance of the present results to the complex experim ental behavior of centrosymmetric kappa-(BEDT-TTF)(2)Cu[N(CN)](2)Y salts is discussed.