Nonadiabatic effects of rattling phonons and4fexcitations inPr(Os1−x

Abstract

In the skutterudite compounds the anharmonic "rattling" oscillations of 4f-guest ions in the surrounding Sb 12 host cages are found to have significant influence on the low-temperature properties. Recently specific-heat analysis of Pr͑Os 1−x Ru x ͒ 4 Sb 12 has shown that the energy of crystalline electric field singlet-triplet excitations increases strongly with Ru concentration x and crosses the almost constant rattling mode frequency 0 at about x Ӎ 0.65. Due to magnetoelastic interactions this may entail prominent nonadiabatic effects in inelastic neutronscattering intensity and quadrupolar susceptibility. Furthermore the Ru-concentration dependence of the superconducting T c , notably the minimum at intermediate x is explained as a crossover effect from pair-forming aspherical Coulomb scattering to pair-breaking exchange scattering.