Distinct Kondo Screening Behaviors in Heavy Fermion Filled Skutterudites with 4f1 and 4f2 Configurations

TL;DR

This study compares the microscopic origins of Kondo behaviors in heavy fermion skutterudites with 4f1 and 4f2 electron configurations, revealing distinct hybridization mechanisms and ground states through advanced spectroscopy.

Contribution

It provides the first detailed microscopic comparison of Kondo screening in heavy fermion skutterudites with different 4f electron configurations using angle-resolved photoemission spectroscopy.

Findings

Strong hybridization in CeOs4Sb12 with band-dependent gaps

Incoherent hybridization in PrOs4Sb12 due to thermally excited CEF states

Direct observation of Kondo insulating state in CeOs4Sb12

Abstract

Filled-skutterudite heavy fermion (HF) compounds host rich ground states depending on the f electron configurations. CeOs4Sb12 (COS) with Ce 4f1, and PrOs4Sb12 (POS) with Pr 4f2 configurations show distinct properties of Kondo insulating and HF superconductivity, respectivity. We unveiled the underlying microscopic origin by angle-resolved photoemission spectroscopy studies. Their eV-scale band structure matches well, representing the common characters of conduction electrons in ROs4Sb12 systems (R = rare earth). However, f electrons interact differently with conduction electrons in them. Strong hybridization between conduction electrons and f electrons is observed in COS with band dependent hybridization gaps, and the development of Kondo insulating state is directly revealed. Although the ground state of POS is a singlet, finite but incoherent hybridization exists due to Kondo scattering with the thermally excited triplet crystalline electric field (CEF) state. Our results help to understand the intriguing properties in COS and POS, and provide a clean demonstration of the microscopic differences in HF systems with 4f1 and 4f2 configurations.