Bandwidth-control orbital-selective delocalization of 4f electrons in epitaxial Ce films

TL;DR

This study demonstrates a novel bandwidth-control orbital-selective delocalization of 4f electrons in epitaxial Ce films through thermal annealing, revealing the interplay between Mott physics and Kondo hybridization.

Contribution

It provides the first experimental realization of bandwidth-control 4f electron delocalization in Ce films and compares it with theoretical predictions, highlighting the coexistence of Mott and Kondo physics.

Findings

Observation of large dispersion quasiparticle bands with 4f character near E_F

Agreement between experimental dispersion and density-functional theory calculations

Unusual temperature dependence indicating interplay between Mott physics and Kondo hybridization

Abstract

The 4f-electron delocalization plays a key role in the low-temperature properties of rare-earth metals and intermetallics, including heavy fermions and mix-valent compounds, and is normally realized by the many-body Kondo coupling between 4f and conduction electrons. Due to the large onsite Coulomb repulsion of 4f electrons, the bandwidth-control Mott-type delocalization, commonly observed in d-electron systems, is difficult in 4f-electron systems and remains elusive in spectroscopic experiments. Here we demonstrate that the bandwidth-control orbital-selective delocalization of 4f electrons can be realized in epitaxial Ce films by thermal annealing, which results in a metastable surface phase with a reduced layer spacing. The resulting quasiparticle bands exhibit large dispersion with exclusive 4f character near E_F and extend reasonably far below the Fermi energy, which can be explained from the Mott physics. The experimental quasiparticle dispersion agrees surprisingly well with density-functional theory calculation and also exhibits unusual temperature dependence, which could be a direct consequence of the delicate interplay between the bandwidth-control Mott physics and the coexisting Kondo hybridization. Our work therefore opens up the opportunity to study the interaction between two well-known localization-delocalization mechanisms in correlation physics, i.e., Kondo vs Mott, which can be important for a fundamental understanding of 4f-electron systems.