We have studied magnetic excitations in impurity-doped La 1.85Sr0.15Cu1-y,AyO4 (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 incommensurability σ - 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 single broad commensurate peak at E cross - 15 meV. Compared with that for the impurity-free sample with a similar Sr concentration of x - 0.16, Ecross for Ni:y - 0.029 is decreased by nearly the same factor as the reduction in TEc. This is very similar to the shift of resonance energy (Eres)in Ni-doped YBa2Cu3O7. These common impurity effects on the shifts of Ecross and Eres suggest the same magnetic origin of the resonance peak in YBa2Cu3O6+x and that of the crossing point of upward and downward dispersions in La 2-xSrxCuO4. We propose that the sudden change in the dispersions is better described by a crossover from incommensurate spin fluctuations to a gapped spin wave rather than an hourglass-like dispersion.
|ジャーナル||journal of the physical society of japan|
|出版ステータス||Published - 2009 11月|
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