Quantum Spin Dynamics of anS=3/2Heisenberg Antiferromagnetic Chain: Inelastic Pulsed Neutron Scattering from CsVCl3

Well-defined spin-wave excitations were observed by using pulsed neutrons from CsVC${\mathrm{l}}_3$, an $S=3/2\mathrm{}$ Heisenberg antiferromagnetic chain. The observed spin-wave dispersion relation shows an enhancement of the excitation energy by a factor of 1.26, which must be compared with the quantum renormalization factor of $\pi /2\mathrm{}$ for an $S=1/2\mathrm{}$ system. The linewidth of the spectrum at 40 K was broad and independent of $q$. The $q$-independent linewidth is the first experimental observation, which was predicted by rigorous theories for a classical chain at sufficiently low temperature.