HOLE DOPING AND DISORDER EFFECTS ON THE ONE-DIMENSIONAL KONDO-LATTICE, FOR FERROMAGNETIC KONDO COUPLINGS

We investigate the one-dimensional Kondo lattice model for ferromagnet ic Kondo couplings. The so-called ferromagnetic two-leg spin ladder an d the S=1 antiferromagnet occur as one-dimensional Kondo insulators. B oth exhibit a spin gap. But, in contrast to the strong-coupling limit, the Haldane state which characterizes the two-leg spin-ladder Kondo i nsulator cannot fight against very weak exterior perturbations. First, by using standard bosonization techniques, we prove that an antiferro magnetic ground state occurs by doping with few holes; it is character ized by a form factor of the spin-spin correlation functions which exh ibits two structures, respectively, at q=pi and q=2k(F). Second, we pr ove precisely by using renormalization-group methods that the Anderson localization inevitably takes place in that weak-coupling Haldane sys tem, by the introduction of quenched randomness; the spin-fixed point rather corresponds to a ''glass'' state, Finally, a weak-coupling anal og of the S=1 antiferromagnet Kondo insulator is proposed; we show tha t the transition into the Anderson-localization state maybe avoided in that unusual weak-coupling Haldane system.