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

概要

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We have studied magnetic excitations in impurity-doped La1.85Sr0.15Cu1-yAyO4 ($\text{A} = \text{Ni}$ or Zn) by neutron scattering. The dispersion for $\text{Zn:$y$} = 0.017$ is similar to that for the impurity-free sample: incommensurate peaks with incommensurability $\delta = 0.12 \pm 0.01$ (rlu) do not change their positions up to 21 meV. On the other hand, for $\text{Ni:$y$} = 0.029$, two incommensurate peaks observed at low energies suddenly change into a single broad commensurate peak at $E_{\text{cross}} = 15$ meV. Compared with that for the impurity-free sample with a similar Sr concentration of $x = 0.16$, $E_{\text{cross}}$ for $\text{Ni:$y$} = 0.029$ is decreased by nearly the same factor as the reduction in $T_{\text{c}}$. This is very similar to the shift of resonance energy ($E_{\text{res}}$) in Ni-doped YBa2Cu3O7. These common impurity effects on the shifts of $E_{\text{cross}}$ and $E_{\text{res}}$ suggest the same magnetic origin of the resonance peak in YBa2Cu3O6+x and that of the crossing point of upward and downward dispersions in La2-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.
Physical Society of Japanの論文
2009-11-15