MAGNETIC EXCITATIONS OF THE DOPED-HOLE STATE IN DIAMAGNETIC LA2CU0.5LI0.5O4

Substitution of Li for Cu in La2Cu1-xLixO4 donates holes; at x = 0.5 t he Li ions form an ordered superlattice which isolates individual CuO4 plaquettes from one another, and the number of doped holes is suffici ent that each plaquette is occupied. Above 170 K, an activated tempera ture dependence of the Cu nuclear spin relaxation rate reveals a magne tic excitation of the doped-hole state with an energy of similar to 13 0 meV. Below 170 K relaxation is primarily due to fluctuations of the electric field gradient; the temperature dependence of this rate is an omalously slow: T-1(-1) proportional to root T.