THEORY OF A SINGLE OXYGEN HOLE PROPAGATING IN SR2CUO2CL2 - THE SPIN OF THE QUASI-PARTICLES IN CUO2 PLANES

Recent photoemission experiments have measured E vs. k for a single ho le propagating in antiferromagnetically aligned Sr2CuO2Cl2. Comparison s with (i) the t - t' - J model, for which the carrier is a spinless v acancy, and (ii) a strong-coupling version of the three-band Emery mod el,for which the carrier is a S = 1/2 hole moving on the Oxygen: subla ttice, have demonstrated that if one wishes to describe the quasiparti cle throughout the entire first Brillouin zone the three-band model is superior. Here we present a new variational wave function for a singl e Oxygen hole in the three-band model: it utilizes a classical represe ntation of the antiferromagnetically ordered Cu-spin background but ex plicitly includes the quantum fluctuations of the lowest energy double t of the Cu-O-Cu bond containing the Oxygen hole. We find that this wa ve function leads to a quasiparticle dispersion for physical exchange and hopping parameters that is in excellent agreement with the measure d ARPES data. We also obtain the average spin of the Oxygen hole, and thus deduce that this spin is only quenched to zero at certain wave ve ctors, helping to explain the inadequacy of the t - t' - J model to ma tch the experimentally observed dispersion relation everywhere in the first Brillouin zone.