Scaling of the spin stiffness in random spin - 1 2 chains Crossover from pure - metallic behaviour to random singlet - localized regime

In this paper we study the localization transition induced by the disorder in random antiferromagnetic spin1 2 chains. The results of numerical large scale computations are presented for the XX model using its free fermions representation. The scaling behavior of the spin stiffness is investigated for various disorder strengths. The disorder dependence of the localization length is studied and a comparison between numerical results and bosonization arguments is presented. A non trivial connection between localization effects and the crossover from the pure XX fixed point to the infinite randomness fixed point is pointed out. PACS. 75.10.Jm Quantized spin models – 75.40.Mg Numerical simulation studies – 05.70.Jk Critical point phenomena – 75.50.Lk Spin glasses and other random magnets