Renormalization of Commensurate Magnetic Peak in Ni-doped La₁.₈₅Sr₀.₁₅CuO₄

الأصل · EN

We have studied the magnetic excitations in impurity doped La₁.₈₅Sr₀.₁₅Cu₁₋yAyO₄ (A=Ni or Zn) by neutron scattering. The dispersion for Zn:y=0.017 is similar to that for the impurity free sample: incommensurate peaks with the incommensurability δ=0.12±0.01 (rlu) do not change their positions up to 21 meV. On the other hand, for Ni:y=0.029, two incommensurate peaks observed at low energies suddenly change into a broad commensurate peak at Ecross=15 meV. Compared to the impurity free sample with a similar Sr-concentration x=0.16, [B. Vignolle et al. Nature Physics 3 (2007) 163], Ecross for Ni:y=0.029 is decreased by nearly the same factor for the reduction in Tc. This is very similar to the shift of the resonance energy (Eᵣes) in Ni-doped YBa₂Cu₃O₇.[Y. Sidis et al.: Phys. Rev. Lett. 84 (2000) 5900]. These common impurity effects on the shift of Ecross and Eᵣes suggest the same magnetic origin for the resonance peak in YBa₂Cu₃Oδ and that for a crossing point of upward and downward dispersions in the La₂₋ₓSrₓCuO₄. We propose that the sudden change in the dispersion is better described by a crossover from incommensurate spin fluctuations to a gapped spin wave rather than a hourglass-like dispersion.