Field dependent mass enhancement in Pr_{1-x}La_xOs_4Sb_12 from aspherical Coulomb scattering

TL;DR

This paper investigates how crystalline electric field excitations cause field-dependent mass enhancement of quasiparticles in Pr_{1-x}La_xOs_4Sb_12, highlighting aspherical Coulomb scattering as a key mechanism.

Contribution

It introduces a theoretical model for mass enhancement via aspherical Coulomb scattering, including dispersive excitations, and predicts field-dependent effects in skutterudite compounds.

Findings

Mass enhancement is strongly field dependent due to triplet splitting.

The model accounts for dispersive excitations affecting quasiparticle mass.

Potential experimental observation in Pr_{1-x}La_xOs_4Sb_12 with large x.

Abstract

The scattering of conduction electrons by crystalline electric field (CEF) excitations may enhance their effective quasiparticle mass similar to scattering from phonons. A wellknown example is Pr metal where the isotropic exchange scattering from inelastic singlet-singlet excitations causes the mass enhancement. An analogous mechanism may be at work in the skutterudite compounds Pr_{1-x}La_xOs_4Sb_12 where close to x=1 the compound develops heavy quasiparticles with a large linear specific heat coefficient. There the low lying CEF states are singlet ground state and a triplet at 8 K. Due to the tetrahedral CEF the main scattering mechanism must be the aspherical Coulomb scattering. We derive the expression for mass enhancement in this model including also the case of dispersive excitations. We show that for small to moderate dispersion there is a strongly field dependent mass enhancement due to the field induced triplet splitting. It is suggested that this effect may be seen in Pr_{1-x}La_xOs_4Sb_12 with suitably large x when the dispersion is small.