We report an inelastic light scattering study of single-crystalline NaCu2O2, a spin-chain compound known to exhibit a phase with helical magnetic order at low temperatures. Phonon excitations were studied as a function of temperature and light polarization, and the phonon frequencies are compared to the results of ab-initio lattice dynamical calculations, which are also reported here. The good agreement between the observed and calculated modes allows an assignment of the phonon eigenvectors. Two distinct high-energy two-magnon features as well as a sharp low-energy one-magnon peak were also observed. These features are discussed in terms of the magnon modes expected in a helically ordered state. Their polarization dependence provides evidence of substantial exchange interactions between two closely spaced spin chains within a unit cell. At high temperatures, the spectral features attributable to magnetic excitations are replaced by a broad, quasielastic mode due to overdamped spin excitations.
@article{arxiv.cond-mat/0511116,
title = {Magnetic excitations and phonons in the spin-chain compound NaCu2O2},
author = {K. -Y. Choi and V. P. Gnezdilov and P. Lemmens and L. Capogna and M. R. Johnson and M. Sofin and A. Maljuk and M. Jansen and B. Keimer},
journal= {arXiv preprint arXiv:cond-mat/0511116},
year = {2009}
}