Experimental observation of a soft mode in ammonium hydrogen oxalate hemihydrate by Brillouin scattering J.P. Benoit, J. Berger, M. Krauzman et J.L. GodetJ. Phys. France, 47 5 (1986) 815-819DOI: https://doi.org/10.1051/jphys:01986004705081500
