Inelastic neutron studies of the low energy phonon excitations in the RENi2B2C superconductors (RE = Lu, Y, Ho, Er)

The authors studied the low-energy phonon excitations for wavevectors close to the Fermi surface nesting vector rvec ξm ≅ 0.55 rvec a. They find that above Tc the frequencies of the Δ4 [ζ00] lowest-lying optical and acoustic phonon modes decrease with decreasing temperature, for rvec ξ close to rvec ξm, and there is a shift of intensity from the upper to the lower mode, an effect characteristic of coupled modes. From approximately 120K down to temperatures in the vicinity of Tc, only a single unresolved peak is observed. Below Tc the phonon spectra of the Y and Lu compounds change dramatically: they consist of a sharp peak at approximately 4.5 meV with a weak shoulder at the higher energy side. No such sharp peak was observed below Tc in the Ho and Er compounds