Physical Review Letters
Dynamics of an S=12 , One-Dimensional Heisenberg Antiferromagnet
Y. Endoh, Gen Shirane, R. J. Birgeneau, Peter M. Richards, S. L. Holt
Abstract
We report a detailed neutron-scattering study of the spin dynamics in Cu${\mathrm{Cl}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}2N(${\mathrm{C}}_{5}$${\mathrm{D}}_{5}$), a physical realization of the one-dimensional $S=\frac{1}{2}$ Heisenberg antiferromagnet. At $T=1.3$ K well-defined excitations are observed over the whole zone with energies given by $E(q)=\ensuremath{\pi}{J}_{\mathrm{nn}}sin(\mathrm{qc})$, 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 $T=8$ K the excitations are broad and ill defined.