Theory of a single oxygen hole propagating in Sr2CuO2Cl2: The spin of the quasiparticles in CuO2 planes

Recent photoemission experiments have measured E vs. k for a single hole propagating in antiferromagnetically aligned Sr2CuO2Cl2. Comparisons with (i) the t - t' - J model, for which the carrier is a spinless vacancy, and (ii) a strong-coupling version of the three-band Emery model,for which the carrier is a S = 1/2 hole moving on the Oxygen: sublattice, have demonstrated that if one wishes to describe the quasiparticle throughout the entire first Brillouin zone the three-band model is superior. Here we present a new variational wave function for a single Oxygen hole in the three-band model: it utilizes a classical representation of the antiferromagnetically ordered Cu-spin background but explicitly includes the quantum fluctuations of the lowest energy doublet of the Cu-O-Cu bond containing the Oxygen hole. We find that this wave function leads to a quasiparticle dispersion for physical exchange and hopping parameters that is in excellent agreement with the measured 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 vectors, helping to explain the inadequacy of the t - t' - J model to match the experimentally observed dispersion relation everywhere in the first Brillouin zone.