Low-energy incommensurate spin excitations in superconductingLa1.85Sr0.15CuO4

Neutron-scattering experiments with markedly improved signal-to-noise ratios have been performed on single-crystal superconducting La[sub 1.85]Sr[sub 0.15]CuO[sub 4] ([ital T][sub [ital c]]=33 K) at energies down to 1.5 meV. The measurements provide quantitative information on the temperature dependence of [chi][prime][prime]([bold q],[omega]). Surprisingly, [chi][prime][prime]([bold q][sub peak],[omega]) is approximately constant below [ital T][sub [ital c]] for the measured energies 1.5 meV[le][omega][le]6 meV, that is, for energies much less than the mean-field BCS gap energy of [similar to]10 meV, hence implying other than conventional [ital s]-wave superconductivity.