Kondo Reshapes Multiple Orders in a $5f$ van der Waals Material

TL;DR

This study demonstrates that in the van der Waals $5f$ material $eta$-UTe$_3$, a heavy-fermion state can compete with charge order, revealing new interactions beyond traditional spin-based competition in correlated electron systems.

Contribution

The paper introduces the observation of heavy-fermion behavior competing with charge density wave order in a $5f$ van der Waals material, expanding the understanding of correlated phases beyond spin interactions.

Findings

Detection of Fano resonances indicating heavy fermion state

Disappearance of Fermi surface nesting and flat band formation

Absence of charge density wave in $eta$-UTe$_3$

Abstract

Electron interactions can drive magnetism, superconductivity, and topology. However, the realization of these phases remains limited in van der Waals materials, and the full landscape of strong correlations remains uncharted in any context. While interactions between conduction electrons and localized spins yield a well-known competition between heavy fermions (Kondo hybridization) and magnetic order (RKKY exchange), such spin-driven competition represents only part of the correlated electron phase diagram. Here we demonstrate that a heavy-fermion state can also compete with charge order, such as the charge density wave (CDW) state typical in the van der Waals $4f$ rare-earth tritellurides (RTe$_3$). We exploit the spatially-extended $5f$ orbitals of $\beta$-UTe$_3$ to enhance Kondo hybridization compared to its isostructural RTe$_3$ cousins. Our scanning tunneling spectroscopy on $\beta$-UTe$_3$ shows Fano resonances characteristic of the heavy fermion state, while our quasiparticle interference imaging reveals the disappearance of Fermi-level nesting and the appearance of flat bands. We extend the tritelluride tight-binding model to include Kondo coupling and quantify the Fermi surface reconstruction. Consistent with the destruction of nesting, we observe no CDW in $\beta$-UTe$_3$. Our expansion of the Kondo phase diagram beyond spin-mediated competition opens new possibilities for proximity-induced phase engineering in correlated van der Waals heterostructures.