| Magnetism of High Temperature Superconductors The discovery of superconductivity in the doped copper oxides has stimulated the study of the magnetism in these materials, both because of its intrinsic interest and its connection to high temperature superconductivity. The undoped parent compounds are antiferromagnetic (AF) insulators. The long-range AF order is rapidly destroyed with doping, and upon further doping the system becomes superconducting, while short-range AF correlations still persist. The copper oxide materials are strongly anisotropic, both with respect to their transport and magnetic properties. It is widely believed that the CuO planes are responsible for the properties of those materials. Doping introduces holes which are the charge carriers in the AF square lattice of the CuO planes. The simplest model that seems to contain the physics of the CuO planes is the t-J model, which describes holes moving in a Heisenberg spin system. In this system the holes are strongly coupled to the spin array, the motion of holes generating spin fluctuations. A striking feature of the copper oxides is the strong sensitivity of their magnetic properties to hole concentration. Our work has been concerned with the understanding of this aspect. We have studied the effects of doping on a set of magnetic properties, namely, spin excitations, susceptibility, and staggered magnetization, within the t-J model. Quantum many-particle techniques were used to calculate the renormalization of the magnetic properties induced by the hole-magnon interaction. We found that those properties strongly depend on doping due to the hole-magnon interaction generated by hole motion, our results showing good agreement with experimental data on the copper oxide high temperature superconductors. | |
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