Different Evolution of Intrinsic Gap in Kondo Semiconductors SmB6 and YbB12

TL;DR

This study investigates how the intrinsic energy gap and spectral functions in Kondo semiconductors SmB6 and YbB12 evolve with temperature and rare-earth substitution, revealing different mechanisms of gap formation.

Contribution

It provides detailed experimental insights into the contrasting evolution of the intrinsic gap in SmB6 and YbB12 under substitution, highlighting different gap formation mechanisms.

Findings

The intrinsic gap in SmB6 remains robust up to x=0.15 Eu substitution.

The gap in YbB12 collapses at x=0.125 Lu substitution.

Different mechanisms of gap formation are suggested for SmB6 and YbB12.

Abstract

Dependence of the spectral functions on temperature and rare-earth substitution was examined in detail for Kondo semiconductor alloys Sm1-xEuxB6 and Yb1-xLuxB12 by bulk-sensitive photoemission. It is found that the 4f lattice coherence and intrinsic (small) energy gap are robust for SmB6 against the Eu substitution up to x = 0.15 while both collapse by Lu substitution already at x = 0.125 for YbB12. Our results suggest that the mechanism of the intrinsic gap formation is different between SmB6 and YbB12 although they were so far categorized in the same kind of Kondo semiconductors.