Inelastic neutron scattering experiments investigating the spin dynamics along the chain direction of an S = 3 / 2 quasi-one-dimensional Heisenberg antiferromagnet CsVCl 3 were performed up to the zone boundary energy. The authors observed the quantum renormalization in the exchange constant and found that the scattering function cannot be described by either the classical delta -function or the quantum Heisenberg model for S = 1 / 2 . The spin excitations have apparent linewidths and they are compared with the theory of the classical isotropic Heisenberg system at finite temperatures.
We used a combination of the quantum Monte Carlo technique and the maximum entropy method to calculate the dynamic structure factor of the quantum Heisenberg antiferromagnet. The dynamics is governed by renormalized damped spin waves and we calculate their frequencies and linewidths. The computed spin-wave dispersion is in quantitative agreement with inelastic-neutron-scattering experiments on
La2CuO4. The low-energy sector exhibits scaling behavior with the characteristic frequency scale, which is inversely proportional to the correlation length.
Well-defined spin-wave excitations were observed by using pulsed neutrons from CsVC
l3, an
S=3/2 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 $\ensuremath{\pi}/2$ for an
S=1/2 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.