The cluster spin-glass phase in La2-xSr(Ba)xCuO4 as precursor of stripes

A cluster spin-glass transition has been identified in La1.97Ba0.03CuO4, thanks to the analogies of the acoustic spectrum of this sample with that of La2-xSrxCuO4 (x=0.03 and x=0.06), which has a well established cluster spin-glass phase. Our measurements are in good agreement with the presence of antiferromagnetically correlated clusters which are separated by hole rich boundaries. These "charge rivers" are thought to be the precursors of stripes.