Inelastic neutron scattering study of the soft phonon branch in deuterated BCCD - Currat, R.; Legrand, J.F.; Kamba, S.; Petzelt, J.; Dvorak, V.; Albers, J. (Elsevier)
Inelastic neutron scattering on deuterated BCCD revealed a transverse acoustic branch of Λ"3 symmetry coupled to a soft polarisation branch Py(k) of same symmetry. As the transition to the incommensurate state is approached from above (T〉T"1 = 164 K), the lowest-frequency branch develops a broad dispersion minimum near k =0.32c^*. The soft mode is observed as an underdamped excitation down to 170K. The present results establish the displacive nature of the phase transition at T"1 and the P y- symmetry of the primary order parameter. A semi-quantitative scheme for the 14 lowest phonon branches along the c^* direction, in the normal phase, is suggested, based on the available neutron-scattering, infrared, Raman, and acoustic data.
http://linkinghub.elsevier.com/retrieve/pii/0038-1098(90)90416-9
Keywords: U