We have used a combination of neutron resonant spin-echo and triple-axis spectroscopies to determine the energy, fine structure, and linewidth of the magnon resonance in the model spin-1/2 ladder antiferromagnet IPA-CuCl_3 at temperatures T << Delta_0 /k_B, where Delta_0 is the spin gap at T=0. In this low-temperature regime we find that the results deviate substantially from the predictions of the non-linear sigma model proposed as a description of magnon excitations in one-dimensional quantum magnets and attribute these deviations to real-space and spin-space anisotropies in the spin Hamiltonian as well as scattering of magnon excitations from a dilute density of impurities. These effects are generic to experimental realizations of one-dimensional quantum magnets.
@article{arxiv.1102.0214,
title = {Low Temperature Dynamics of Magnons in a Spin-1/2 Ladder Compound},
author = {B. Náfrádi and T. Keller and H. Manaka and A. Zheludev and B. Keimer},
journal= {arXiv preprint arXiv:1102.0214},
year = {2015}
}