Light scattering from magnetic-energy fluctuations in the one-dimensional Heisenberg antiferromagnetKCuF3

Inelastic light scattering by magnetic-energy fluctuations has been observed in the one-dimensional Heisenberg antiferromagnet ${\mathrm{KCuF}}_3$ using a conventional Raman spectrometer. The scattering, having a peak in the cross section at zero frequency and completely distinguished from Rayleigh scattering, is observed over an extremely wide range of temperature above ${\mathit{T}}_{\mathit{N}}$=39 K. The scattered light is strongly polarized and its line profile around zero frequency is well fitted on a Lorentzian curve. The cross section increases with increasing temperature above ${\mathit{T}}_{\mathit{N}}$. Our experimental data are well explained by the theory which Halley developed introducing the hydrodynamic form for the correlation function of magnetic-energy density given by Halperin and Hohenberg. The absence of such inelastic scattering in ${\mathrm{K}}_2$ ${\mathrm{CoF}}_4$ (a two-dimensional Ising antiferromagnet) and ${\mathrm{K}}_2$ ${\mathrm{CuF}}_4$ (a two-dimensional Heisenberg ferromagnet) in a Raman spectrum is also discussed.