Dynamics of the Singlet-Triplet System Coupled with Conduction Spins -- Application to Pr Skutterudites

TL;DR

This paper investigates the finite-temperature dynamics of singlet-triplet systems coupled with conduction electrons, revealing how Kondo effects and spectral features evolve with temperature and crystal field splitting.

Contribution

It applies the non-crossing approximation to analyze the interplay between Kondo physics and crystal electric field effects in Pr skutterudites.

Findings

Kondo effect appears at temperatures above CEF splitting despite low Kondo temperature.

Inelastic peaks develop at low temperatures when CEF splitting suppresses the Kondo effect.

Broad quasi-elastic neutron scattering spectra are explained by parameter ranges where CEF splittings are negligible.

Abstract

Dynamics of the singlet-triplet crystalline electric field (CEF) system at finite temperatures is discussed by use of the non-crossing approximation. Even though the Kondo temperature is smaller than excitation energy to the CEF triplet, the Kondo effect appears at temperatures higher than the CEF splitting, and accordingly only quasi-elastic peak is found in the magnetic spectra. On the other hand, at lower temperatures the CEF splitting suppresses the Kondo effect and inelastic peak develops. The broad quasi-elastic neutron scattering spectra observed in PrFe_4P_{12} at temperatures higher than the quadrupole order correspond to the parameter range where the CEF splittings are unimportant.