Lattice dynamics of YCu2

Lattice dynamics and the interaction with the crystal electric field in NdCu2

“…As the primitive cell consists of six ions, there are 18 phonon branches, which show no degeneracy along the three main symmetry directions. Nine of these branches are Raman active [21] at the -point (a discussion of the lattice dynamics of the isostructural YCu 2 compound can be found in [19]).…”

“…Since there are 15 optical phonon branches within a comparatively narrow energy range of about 10 meV, additional information is needed to classify the measured phonons with respect to their symmetry. From the inelastic one-phonon neutron scattering cross section it follows that the structure factor depends on the scalar product of the scattering vector κ and the polarization vector of the phonon e qν,i [19]. In the following we use κ = Q + q, for a scattering vector in the extended zone scheme.…”

“…In order to calculate phonon dispersion relations a Born-von Karman model with 20 fitting parameters was applied. As starting parameters for the fit procedure the spring constants for YCu 2 given in [19] have been used. It follows from symmetry considerations that for each of the three main symmetry directions there exist four irreducible representations.…”

“…After we finished the study of the lattice dynamics of the isostructural nonmagnetic YCu 2 compound [19] we continued to investigate also the lattice dynamics of the RCu 2 compounds beginning with NdCu 2 . We expected that if a CEF-phonon interaction in NdCu 2 is detectable in neutron experiments, it should be observable when studying the temperature variation of either the lattice dynamics or the CEF excitations.…”

Comparison of the CF-induced phonon shifts in CeCu2 and NdCu2

“…The phonon eigenvectors used in the calculation are obtained from the phonon dispersion relation, which is known for YCu 2 [6] and NdCu 2 [2]. Our calculation was done in a point charge model, and the softening of the CF levels was not taken into account for the calculation of the phonon softening.…”