Low-energy phonons in TbNi2B2C and HoNi2B2C

We report inelastic neutron-scattering experiments on RNi2B2C single crystals (R=Tb and Ho) to investigate the dispersion of low-energy phonons. Both compounds order antiferromagnetically at low temperatures. For superconducting HoNi2B2C we observe a strong softening of two phonon branches similar to other superconducting RNi2B2C compounds. In contrast, for the non-superconducting TbNi2B2C we could not detect significant changes in the phonon spectra as a function of temperature. This correlation between superconductivity and the observed phonon softening indicates a strong electron-phonon interaction and strongly supports the BCS-like description of these compounds.