Two-magnon Raman scattering in (La1-xSrx)2CuO4

The two-dimensional two-magnon peak in (La1-xSrx)2CuO4 decreases rapidly from x=0 to x=0.01. For x>0.03 scattering is observed over a very wide energy region from low energy to over 4000 cm-1. This indicates that the correlation length of the two-dimensional spin order decreases rapidly from x=0 to x=0.01. This decrease can be related to the rapid decrease of the three-dimensional antiferromagnetic transition temperature (TN), while at x>0.03 the correlation still retains a short length and a short time. At x<0.01 the scattering is in a resonant state with narrow electronic levels of which transition energy is about 18 000 cm-1. The narrowness of these energy levels, and the simultaneous extinction of resonance and the two-magnon scattering, suggest that these are localized levels relating to the Cu spins.