Observation of the Haldane gap in RbNiCl3.

TLDR: L'application de la theorie du champ de Affleck a RbNiCl 3 montre que cette theorie est a mesure d'expliquer la dispersion du mode du gap et son intensite relative au voisinage du vecteur d'onde de la mise en ordre tridimensionnelle.

Abstract: The Haldane gap is observed by neutron scattering in ${\mathrm{RbNiCl}}_{3}$. The three-dimensional-phase magnetic spectrum of ${\mathrm{RbNiCl}}_{3}$ is found to be very similar to that of ${\mathrm{CsNiCl}}_{3}$, even though the two materials differ significantly in the exchange parameters. Application of Affleck's field theory to ${\mathrm{RbNiCl}}_{3}$ shows that the theory is capable of explaining the dispersion of the gap mode and its relative intensity near the three-dimensional ordering wave vector (1/3,1/3,1). However, the theory does not provide a satisfactory explanation for the nearly degenerate magnon frequencies at (0,0,1). We argue that the degeneracy at (0,0,1) may not be related to the existence of the Haldane gap in integer-spin systems. Rather, it could be a general feature of certain antiferromagnetic materials.