Large Fermi Surface Expansion through Anisotropic c-f Mixing in the Semimetallic Kondo Lattice System CeBi

TL;DR

This study uses ARPES techniques to reveal a significant Fermi surface expansion in CeBi driven by anisotropic c-f electron mixing and small valence changes, indicating charge fluctuations in a low carrier density Kondo system.

Contribution

It provides direct experimental evidence of a large Fermi surface change caused by anisotropic c-f mixing and small valence fluctuations in CeBi, a low carrier density Kondo lattice.

Findings

Fermi surface volume expands up to 40% at low temperature.

Spectral weight transfers from Ce 4f to conduction bands.

Large FS change explained by ~1% Ce valence shift.

Abstract

Using angle-resolved photoemission spectroscopy (ARPES) and resonant ARPES, we report evidence of strong anisotropic conduction-f electron mixing (c-f mixing) in CeBi by observing a largely expanded Ce-5d pocket at low temperature, with no change in the Bi-6p bands. The Fermi surface (FS) expansion is accompanied by a pronounced spectral weight transfer from the local 4f 0 peak of Ce (corresponding to Ce3+) to the itinerant conduction bands near the Fermi level. Careful analysis suggests that the observed large FS change (with a volume expansion of the electron pocket up to 40%) can most naturally be explained by a small valence change (~ 1%) of Ce, which coexists with a very weak Kondo screening. Our work therefore provides evidence for a FS change driven by real charge fluctuations deep in the Kondo limit, which is made possible by the low carrier density.