UNIVERSAL CHARGE AND SPIN RESPONSE IN OPTIMALLY DOPED ANTIFERROMAGNETS

Charge and spin response in the planar t-J model at finite temperature s are investigated numerically, in the regime corresponding to cuprate s at intermediate doping. We show that the local spin correlation func tion is T independent, leading to chi(11)(omega < J) proportional to t anh(omega/2T). The current correlation function C(omega) appears to be T as well as omega independent, and the optical conductivity sigma pr oportional to (1 - e(-omega/T))/omega. Such anomalous response functio ns are brought in connection with the large entropy persisting at T < J.