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

Yi Wu,Peng Li,Yang Liu,Zhiguang Xiao,Hao Zheng,Huiqiu Yuan,Chao Cao,Yuan Fang,Yi-feng Yang

doi:10.1038/s41467-021-22710-2

Abstract

The 4f-electron delocalization plays a key role in the low-temperature properties of rare-earth metals and intermetallics, and it is normally realized by the Kondo coupling between 4f and conduction electrons. Due to the large 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 reduced layer spacing. The quasiparticle bands exhibit large dispersion with exclusive 4f character near bar{{{Gamma }}} and extend reasonably far below the Fermi energy, which can be explained from the Mott physics. The experimental quasiparticle dispersion agrees well with density-functional theory calculation and also exhibits unusual temperature dependence, which could arise from the delicate interplay between the bandwidth-control Mott physics and the coexisting Kondo hybridization. Our work 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.

Highlights

The 4f-electron delocalization plays a key role in the low-temperature properties of rare-earth metals and intermetallics, and it is normally realized by the Kondo coupling between 4f and conduction electrons
Rare earth metals and intermetallics are prototypical strongly correlated electron systems and host a variety of interesting quantum phases, including heavy fermion, quantum criticality, unconventional superconductivity, etc[1,2,3,4,5]. Key to understand these exotic phases lies at unraveling the peculiar nature of the 4f-electron delocalization, which is often described by the periodic Anderson model (PAM) composed of localized 4f electrons and dispersive conduction bands
The single-crystal Ce films are grown by molecular beam epitaxy (MBE) on epitaxial graphene layers and in situ angle-resolved photoemission spectroscopy (ARPES) measurements were performed immediately after film growth

Summary

Introduction

The 4f-electron delocalization plays a key role in the low-temperature properties of rare-earth metals and intermetallics, and it is normally realized by the Kondo coupling between 4f and conduction electrons. Rare earth metals and intermetallics are prototypical strongly correlated electron systems and host a variety of interesting quantum phases, including heavy fermion, quantum criticality, unconventional superconductivity, etc[1,2,3,4,5] Key to understand these exotic phases lies at unraveling the peculiar nature of the 4f-electron delocalization, which is often described by the periodic Anderson model (PAM) composed of localized 4f electrons and dispersive conduction bands. We uncovered a hitherto unreported metastable phase of Ce, where sharp dispersive quasiparticle bands with pure 4f character can be observed near EF, accompanied by an appreciable dispersion of the lower Hubbard band Such spectral character, which cannot be explained by the Kondo hybridization picture, can be well accounted for by the bandwidth-control Mott physics

Methods

Results

Conclusion