Dynamics of anS=12, One-Dimensional Heisenberg Antiferromagnet

Abstract

We report a detailed neutron-scattering study of the spin dynamics in Cu${\mathrm{Cl}}_2$·2N(${\mathrm{C}}_5$ ${\mathrm{D}}_5$), a physical realization of the one-dimensional $S=\frac{1}{2}$ Heisenberg antiferromagnet. At $T=1.3\mathrm{}$ K well-defined excitations are observed over the whole zone with energies given by $E\left(q\right)=\pi J_{\mathrm{nn}}sin\mathrm{}\left(\mathrm{qc}\right)\mathrm{}$, the celebrated des Cloizeaux-Pearson exact solution for the spectrum of first excited states, but with intensities approximately those expected from classical spin-wave theory. At $T=8\mathrm{}$ K the excitations are broad and ill defined.