NMR and neutron-scattering experiments on the cuprate superconductors: A critical re-examination

Abstract

We show that it is possible to reconcile NMR and neutron-scattering experiments on both La2−xSrxCuO4 and YBa2Cu3O6+x, by making use of the Millis-Monien-Pines mean-field phenomenological expression for the dynamic spin-spin response function, and re-examining the standard Shastry-Mila-Rice hyperfine Hamiltonian for NMR experiments. The recent neutron-scattering results of Aeppli et al. onLa1.86Sr0.14CuO4 are shown to agree quantitatively with the NMR measurements of T163 and the magnetic scaling behavior proposed by Barzykin and Pines. The reconciliation of the O17 relaxation rates with the degree of incommensuration in the spin-fluctuation spectrum seen in neutron experiments is achieved by introducing a transferred hyperfine coupling C′ between O17 nuclei and their next-nearest-neighbor Cu2+ spins; this leads to a near-perfect cancellation of the influence of the incommensurate spin-fluctuation peaks on the O17 relaxation rates of La2−xSrxCuO4. The inclusion of the C′ term also leads to a natural explanation, within the one-component model, the different temperature dependence of the anisotropic O17 relaxation rates for different field orientations, recently observed by Martindale et al. The measured significant decrease with doping of the anisotropy ratio, R63=T1ab63T1c63 in the La2−xSrxCuO4 system, from R63=3.9 for La2CuO4 to R63≃3.0 for La1.85Sr0.15CuO4 is made compatible with the doping dependence of the shift in the incommensurate spin-fluctuation peaks measured in neutron experiments, by suitable choices of the direct and transferred hyperfine coupling constants Aβ and B.

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