Nonadiabatic effects of rattling phonons and 4f excitations in Pr(Os{1-x}Ru{x})4Sb12

TL;DR

This paper investigates how anharmonic rattling phonons and 4f electronic excitations in Pr(Os{1-x}Ru{x})4Sb12 influence low-temperature properties, revealing nonadiabatic effects and a crossover in superconducting behavior related to Ru concentration.

Contribution

It demonstrates the impact of nonadiabatic effects due to rattling phonons and 4f excitations on neutron scattering, susceptibility, and superconductivity in Pr(Os{1-x}Ru{x})4Sb12.

Findings

Crystalline electric field excitations increase with Ru concentration.

Rattling mode frequency crosses CEF excitation energy at x ~ 0.65.

Superconducting Tc shows a minimum at intermediate x due to scattering crossover.

Abstract

In the skutterudite compounds the anharmonic 'rattling' oscillations of 4f-host ions in the surrounding Sb12 cages are found to have significant influence on the low temperature properties. Recently specific heat analysis of Pr(Os{1-x}Ru{x})4Sb12 has shown that the energy of crystalline electric field (CEF) singlet-triplet excitations increases strongly with Ru-concentration x and crosses the almost constant rattling mode frequency $\omega_0$ at about x ~ 0.65. Due to magnetoelastic interactions this may entail prominent nonadiabatic effects in inelastic neutron scattering (INS) intensity and quadrupolar susceptibility. Furthermore the Ru- concentration dependence of the superconducting Tc, notably the minimum at intermediate x is explained as a crossover effect from pairforming aspherical Coulomb scattering to pairbreaking exchange scattering.