Antiferromagnetic spin correlations in insulating, metallic, and superconducting La2−xSrxCuO4

Abstract

We have carried out elastic, quasielastic (∫ dE), and inelastic neutron scattering studies of the antiferromagnetic spin correlations in La2−xSrxCuO4 with x varying between 0.02 and 0.18. The crystals, which were grown in three different laboratories, exhibit behavior that varies smoothly with x. In all cases, antiferromagnetic correlations with a scattering amplitude corresponding to a fully occupied Cu2+ square lattice are observed. However, the Néel state is destroyed by the doping and the spin-spin correlation length ξ is quite short, varying from ∼35 to ∼8 Å as x varies between 0.02 and 0.18; the local order is, however, the same as in pure La2CuO4. The fluctuations are dynamic in character as in La2CuO4 above the Néel temperature TN. To a first approximation, ξ=3.8x Å, the average separation between the holes introduced by the Sr2+ doping. The x=0.08 sample exhibits superconductivity with Tc=10 K and with a Meissner fraction exceeding 15% at 5 K; no important differences in the magnetic scattering are observed in the normal and superconducting states. In an appendix we present additional data on the spin dynamics in pure La2CuO4 at Tc=300 K in a sample with TN=235 K.

Source-reported materials — not catalogue approval

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